It doesn't matter, as long as it's pretty much the same time every day. The key is that you never slip below the minimum at any point between doses. If minimum FC for your CYA is 4, and you target 6 and the next day it's at 3.5, you need to target 6.5 the next day so it never drops below the minimum. And sadly, you can't just double up and skip a day, because it's not a fixed PPM per day; the loss is a percentage of the starting, so you lose more at higher FC levels.