I have a 72 cell thing of all petunias
If they are reaching the top of the "green house" then remove the cover. It is supposed to be vented for a while before hand as you want to keep the seedlings warm until they reach a certain height and thickness. Keeping the heat in, but venting and not over heat. Then when they are big enough you completely remove the cover.
East window seems to be the best for me, it gives the most sunlight as it gives you all the morning, and most of the afternoon/day until the sun starts dipping west, that said west would probably be ok too, but not until later in the spring/early summer. When the days are longer and the sun is closer.
I had a neighbor who put her plants in a south window and they did really great there.
That's how I always kill mine off. Take them out to early and forget about them at night - then the frost gets them and they're gonners! :( I will be starting my seeds in the next day or two. I figured even though I am "late" I will still have plenty of time as most of them are later to harvest items.