Our rule was that every time anyone had to use the toilet, everyone had to use the toilet. Went 15 minutes ago? That's OK. Everyone goes when anyone goes.
Every kid is different as far as bladder maturity goes, but if my 6yo (who hates public bathrooms, and will claim that she does not need to go) wet herself while standing in line, we'd be spending the rest of the day back at the resort in the room, where she wouldn't have to worry about being too far from the bathroom to make it.
The only time we've come close, we had to squirm up through about 20 people to the front of the TOT line, ask to be let down the chicken elevator, and run (me carrying her) to the not-at-all-close-to-there bathroom. That was when she was 4, and it made me much stricter with the "everyone goes when anyone goes" rule.