Ahhh, gottcha. Wasn't exactly entirely clear on what you were saying....I probably need a little more tea. xD;
Anyway, if you haven't changed any of them in over a week, then I agree with Callistra. You can go a couple extra days on the larger tanks, but any more then that would be stretching it.
Try and see if you can take an extra few minutes to do your other tanks today as well, though your three gallon would be a priority since it is so small and needs twice weekly partial changes anyway. If you really can't manage to get to them at all today try for early tomorrow if you can, definitely keep a close eye on your levels and maybe add a few extra drops of Prime.