Holding limits

I have been curious about how the models know for how long they will be able to hold their pee during a shoot. I mean, if I would hold it today I will not have any idea when I am going to loose control. Surely after a few wettings the models will get to know their holding capacity but is it like that in the beginning also?
Perhaps some of the models can give us their opinions on this if possible.
Looking forward to hearing the opinions out there.
I'm not a model but I guess they all have different holding capabilities. No doubt some can hold for ages and pee on demand whilst others have to drink a lot of water, tea, coffee, energy drink - or whatever else has a powerful diuretic effect on them - more or less immediately prior to the shoot. Although one should always assume a fair amount of smoke and mirrors when making clips in the adult industry is concerned, I suspect there are adult actresses/pornstars out there who can pee to order and are equally comfortable holding it for several hours or performing 2-3 times an hour even. Bladders vary enormously as do people's skills in voiding them. Although my holding abilities are pretty finite, I'm one of those 'lucky' individuals who can release a controlled amount of pee and then 'clamp off' to avert a full on accident. I know other people of both sexes who can hold for hours on end but once they start it's an unstoppable torrent.