I don't think you have too much to worry about. The only issues would be heat from the lights and a long light cycle will make algae grow faster if it is present. Being that it only happened one day, no harm no foul. If you already have a timer, check to see if it has skipped its programming and needs to be reset. If you do not have a timer I would run out and get one for each light plug you have and get it programmed up and you won't have to worry about leaving your lights on again.