The point is that not all clothepins are alike. Some are deadly, & others you can wear for ages.

It's not possible to bring science into it, but IMO 20 min is enough.

One thing I say to any girl I play with, is that 'you have a responsibility to your own safety.' I say that regardless of what I may ask them to do, their own health & safety comes first.

I think it's a mistake to have too much faith in your Dom- particularly when starting out. With the best of intentions anyone can make a mistake- this is not a science. Anyone who says otherwise may have a list of 'qualifications' as long as your arm, but everyone's pain threshold is different, & dare I say no two nipples are alike(!)

I found in an online session it's essential to first say 'Ultimately you are in charge- I may be cut off or be attacked by an angry wife'

I also have a pen & paper- & write down times & every item of restraint.

Oh & btw- I think it's a mistake to have too much faith in your Dom.....
(yes I did repeat that....)
A big big mistake- ultimately you are in charge of your own destiny.

Tojo