You can leave them or pinch them off neither will hurt the plant. Next year start them later. Marigolds only take about a month from seed to flower and it's a shame to not have them flowering outside instead of inside.

I'd say in your zone it will be the end of May before you can plant them out

Thanks Oilpainter.

I'm going to be watching the forecast really closely. Since these are the first thing I've started from seed indoors, I sure don't want to put them outside too soon.