Is it alright to switch time schedules?

Ive currently have my plants on a 18/6 light schedule, i was wondering if its going to hurt the plants if i switch them to a 24/0 schedule or make them into a hermi? There only 4 inches tall, and unfortantley my buddy is taking the timer so ill be stuck with out one until i make the trip to the local hardware store.

nah they're in veg they should be fine for a day or two. But how long does it take you to go to the hardware store??