I just got two baby Leopard Geckos and I only have a Zoo Med heat rock for them to use until I can get a under-the-tank heater in a few weeks. Will this be too hot for them? It's new and it worked fine for our beardie, I used a temp gun on it and it was 100 degrees. I do have a heat lamp to use during the day, but i'm worried about them being cold at night when I turn the light off.

Heat rocks are not reliable. They can malfunction and injure if not kill the geckos. They are not worth the risk. Them being slightly cooler at night is far better then having their bellies burned.

I have 3 leopard geckos
Research

you should put it on a timer to it runs every 2 hours at night.

DO NOT USE A HEAT ROCK IT WILL BURN THEM UP!!!!!!!!!!!! Leopard geckos get all there heat from there bellies so if you have there bellies at 100 degrees they will burn and probably die.So get a heat mat as soon as you can just don't let the poor lizards die. I would say the only way to keep them alive is to use the heat lap. Good luck!

Leopard gecko owner and research!

DO NOT USE HEAT ROCKS. They are extremely unreliable and I'm sure if you do a quick search you can find multiple images of horrible burns caused by them. They do not distribute heat properly and that creates hot spots which can cause serious injury. Use the heat lamp. What temperature does it get to at night? If it drops to 70 at night than that is perfectly fine, they are used to taking a temp drop at night. It should be about 90 on the hot side during the day time.