A lot of European places outside of England seem against neutering any animal in my experience.
It isn't torture and carries minimal risk of anaesthetic. I've neutered three males and spayed one female and they all came through. The boys didn't really change in behavior, they're the same. They are still crazy love able and all that they were before.
Every animal has diffrent personalities, as a whole they tend to be calmer then girls but they can still be crazy in their own ways. Surgery is alway risky and you always run the risk of complications, so there are a lot of people who dislike risking surgery unless there is a need. Females have more of a health benifit but it's riskier, more invasive and costly. I'd rather fix a boy then a girl, but I am paranoid about surgery. I've lost a guinea pig to post op complications, and that was with an experience vet and after care. I personally don't like neutering or spaying without reason, but calling it torture is a bit mellow dramatic... Having a mixed mischeif or hormonal problems or health complications can be good reasons to neuter.
If you are housing them separately, there is not a need to neuter unless the males are acting overly agressive due to hormones. I house both genders in the same room (separate cages) and have never had any issues. I personally wouldn't risk it unless there is a good reason (i.e. those listed above).
I had to spay my girl because she was supposed to be a boy and it was either give her back to the snake food breeder or get her spayed...easy decision. I think as long as there's valid reason it's fine to spay/neuter.
Speaking from fresh experience : my male ratty was neutered two days ago, and there were no problems at all. He is recovering very fast. On the second day he was ready to run around the room. The scar looked bad for the first 24 hours after surgery, but it heals so unbelievably quickly, and he doesn't seem to be in much pain. I think the whole surgery was more stress for me than him. Of course there are always dangers, but it's the responsible thing to do, and turns out for good in the long run.
My boy Pooka didn't think it was torture as far as I can tell. XD He recovered quickly, though he had two slight complications following surgery. He messed with it and caused the incision to bleed briefly, but that healed on its own. He also developed a small mass around the site that was an abscess, which happens sometimes. I took him to the vet for it, the vet popped it and drained it, put him on antibiotics, and it was healed within two days.
If your rats have has a lot of respiratory issues, surgery is a lot higher risk as it suppresses their breathing (with anesthesia). If their breathing is already compromised, it could cause them to stop breathing. For example, my girl Cream was covered in tumors and the vet suspected they spread to her lungs. I decided putting her down was the best option as she could barely breath, but when they sedated her (so she wouldn't feel the final injection), she stopped breathing all together. However, my girl Silver suffered from URIs all her life and made it through an emergency spay. My boy Bartok also had breathing problems and he survived surgery as well. It really depends, but if your rat is in good health, the risk is lower. I do know of one person who used to be on this forum that got a very young boy neutered and the rat didn't survive. I don't know why.
I believe nanashi was saying her boys are crazy lovable. Not crazy, lol.
My neutered boy is amazing. His fur is soft and free of buck grease. He's lovable, though not cuddly yet. He gets along great with Anya, his female cagemate. He's an awesome shoulder rat. I don't know if neutered changed his personality any, but it did eliminate two things and the possibility of something else. Buck grease is gone, as are the rather large... parts... he had. He also has no chance of developing hormonal aggression, which three of my four previous intact males suffered from. It is also possible that his urine smells less than intact males, but it's hard to know. When I had intact males, I had eight total rats: 4 females, 4 males. And I didn't always keep up with cage cleaning as I should have. Now I just have three rats, two females and a neutered male, so I can't compare.
In September I neutered my two boys at 4.5mo old and they were pretty much back to normal after about 3-4 days. My vet gave me pain meds to keep them comfortable while they healed and help them not mess with it. They were sleepy from that but only needed it for 2 days after the day of the procedure. They were a little swollen back there, but they didn't get abscesses. I took out their litter box and covered anything that could catch/irritate their stitches with fleece, too.
After almost two months, Rupert (very hyper and loves to tussle) didn't change in behavior much, but I would say it dialed down his urge to play-fight and power groom his brother. Before the neuter it was almost constant, I would pet him and he would get super stimulated and tackle his brother, who would immediately start squeaking and showing his belly. Theo is a very vocal rat but you could tell he was just like "ok! You're the alpha! Whatever!". It was also annoying because I couldn't see much more of his personality than that playful hyperness.
That has been cut in half almost, being in a bigger cage the last month helped him even more (he doesn't like the wheel).
Theo actually changed a lot, he became more confidant and seemed happier/more calm. That happiness doubled when he moved into the big cage and now he is the happiest rat ever. He just looks happy and curious all the time Still skittish with noises, but he recovers quickly. I think Rupert having less hormones (and less urge to dominate) plus his own hormones not stressing him out (the girls cage was pretty close and they could smell each other) helped Theo a bunch. Also having other rats to interact with.
With all that said, I don't think they went through any more torture than someone goes through when getting their wisdom teeth taken out...
Id give it 2 weeks to be safe but I've read studies that show most males are entirely sterile by 8 days.
neutering carries benefits and risks. There's a lot of studies that show that neutered males live on average longer healthier lives than entire rats. testosterone does shorten lives by at least a few months in most cases. It also protects against some illnesses though not as directly as spaying a girl.
In the main neutering is a minor operation, it's a lot less invasive than a spay, more akin to a minor lumpectomy Useually with a smaller wound at the end. It does involve anesthetic though so is higher risk for rats with heart or lung issues and some rats do respond badly to being under and can die in surgery or soon after. finding a vet who does neuters on rats ideally or other small exotics minimises this as they will know to use isoflorine gas and such. They will also often do a neater job. My neutered rats look really tidy when done but i saw one person rat that looked butchered. a neat op site is less likley to become infected which is the next risk woth surgery though Thankfully these are usesually minor infective and easily got rid of with a course of antibiotics woth minimum fuss to the rat.
In terms of the neutered rat they generally bounce back in no time. My neuters boys go straight back in with thete cage mates once they have come round and eaten. They tend to be a little tender for the first day or two but then perfectly fine. It can often really help and relax then if they are tense and hormonal and i would do it for any rat who was struggling to manage there hormones for more than a few weeks. i Di think theta a good argument for elective neutering though i prefer to leave it until at least 6 months old though to give the boys chance to fill out a bit first. I'd neuter a boy over a girl if there was a situation where i needed a mixed group. spaying is much more invasive and painful though the health benefits are good too.