What's the room temp and what fish do you have? If the room and tank temp is staying in the 72 degreees and up, it will probably be fine for a day, it really depends on the fish. Does everyone look ok?
Unless it's really cold where you are, it's not the temperature that is as important as the rate at which it drops. If it goes down slowly, it will probably be ok at around 70 degrees. Less than that I'd be worried.
it's ok, i forgot to re-plug the heater in after cleaning the tank and only noticed the next day, the light had been on and all the fish were fine, I find that the light keeps the tank warm enough...