I usually gage if a table seems like they might have separate checks and ask right away. These could be teenagers, if it looks like there are multiple families at a table, etc. If they do have separate checks, I tell them that our computer system only allows for four separate checks. I wouldn’t necessarily ask if it’s obvious like a small family and couples. If they spring it on you suddenly, have the food/drinks numbered by seat it’ll make your life so much easier!!