Which is your FMU if you get up multiple times per night?

I'm the kind of person that always gets up at least once in the middle of the night to pee. Sometimes I get up 2-3 times per night. It's always been like that. Now that I'm in the business of peeing on multiple sticks, I'm confused as to which morning urine is my 'first'. I've read some that say "after your longest stretch of sleep" but I figure, if I sleep for 3 hours then get up to pee, how am I supposed to know at that time if that would be my longest stretch or not? Does anyone else get where I'm going with this and how I should go about getting my "FMU"? via /r/tryingforanother http://ift.tt/2skdBpl