Ooh! What a great thread.
I agree that 30 minutes is probably the optimal sweet spot, but of course it depends on the severity of the offense and what type of corner time you’re doing. If you’re doing it just standing then yes certainly anything past an hour starts to become cruel and counter-productive in my opinion (although sometimes in fantasy, even the prospect multiple hours can be quite exciting!)
If you’re doing something like having to stand on your toes or kneeling, especially kneeling on something, then I’d say 10-15 minutes is best. Anything past 20 becomes extremely difficult and probably not good for your body. If the sub is allowed to sit on the floor or on a stool or something, then an hour is perfectly acceptable.
In any case, even 15 minutes in the corner can sometimes feel like you’ve been there for much, much longer.
There was one time when I was growing up that my mom made me sit in the corner literally all day. I was allowed up for meals and water and to go to the bathroom, but I had to ask permission. I detailed that story in a different thread. Definitely one of the longest days of my life, but of course perfect form wasn’t really expected especially as the day went on.
In my dynamic, “typical” corner time tends to be 20-25 minutes standing, with my hands on my head. Sometimes she’ll have me put my hands behind my back, or hold them straight down the sides of my body. If she doesn’t specify then sometimes I’ll just have them in front of me or use them to cushion my face if I’m resting my head on the wall. I try not to chew on my nails from feeling nervous because she really doesn’t like when I do that!