I've started some indoors as well. I started mine on Mar 18th,
under my plant lights, and yesterday was the very first showing of rootlets coming from the seed. That is 11 days. (this is one of the longest times I've had this season, in fact).

This will give you a time frame to watch for the beginning sprouts.
If it is cooler where you are it might take longer. (it is 70 degrees in my seed starting room here). They are very small when they first come up. Then they turn silver when the first true leaves begin.

If the seeds dry out, they will not germinate. So you have to watch that factor, which is critical. That is why I do alot indoors where I can have control. If they don't work, I have plenty more.

It has been rather difficult here, I had to bring in my 4 flats that I was hardening off back inside, where I have NO ROOM to put them. So we have a portable table set up in the kitchen, and one light system on the dining room floor! I am hoping after today, the warming will stabilize and I can leave them outside.
I also have to move some of the butterfly weed, up into larger containers, but I can't do that while it is soooo cold out! meh!