Light timer broke during seedling stage

No, It’s a plant and all this 18/6, 12/12 stuff are numbers you can follow, but it’s definitely not 100% accurate. Also only you can really tell how it influenced your plant. Even the most experienced growers can’t give you the perfect numbers for seedlings they grow so fast and in the early stages their needs change on a daily basis and also have a genetical factor who could switch all that up a bit. Observe your plant, she will show if she stressed(droopy leaves if lightshedule is way off a healthy Dosis, in nighttime they btw always drop because they sleep and they need 30-120mins to wake back up/stand back up in the morning). And it’s hard to give a seedlings less light than needed, since he doesn’t need much. 12/12 150 watts is the same than 18/6 100 watts. But the 150 watts is better since they have more nighttime to relax. 100watts on 18/6 are only better if you can’t keep humidity and temperature in range, because your light obviously produces more heat with 150 watts and can make your grow room potentially uncontrollable in the terms tempand humidity

Likely not much. I would just leave it on 24 hours till your new timer in. Then set your new start time. Get them back on track then.

i wouldn't worry to much since they are still in a germination phase it will not vause any trouble later on (: beat of luck and sweet smokes 🌱💨

No, it will not cause problems, your seedlings will be absolutely fine.

In the short term it's not really gonna matter. A photoperiod seedling won't flip until they're about 4 weeks old at the earliest and it takes sustained 12/12 cycles for about two weeks to initiate a flip to flower. Some will caution about hermaphrodism but honestly if your genetics are sound it's not likely.