I think is just before during and just after. I could be wrong but I am sure that is how it works, the difference is astounding thou as you can weigh as much difference as 1lb to 5/6 lb.
But when it is your weigh in and it is TOM if you gain or stay the same, mention it and they will write it on your form so that there is a reason for it.
I'm sure there will be someone along soon that knows for definate about the weight difference....x