Having a greenhouse is like having a baby. You have to carry it psychically with you at all times and be mindful of its hourly health.
At nighttime, you don't want it to become too chilly, so you make sure it's warm enough and add extra heat if necessary. During the day, you don't want it to become overheated, so you might have to open all the vents, windows, and doors.
Water at least 2 times a day on sunny days. And protect those baby seedlings from catching any bugs. Give them vitamins (e.g., fish emulsion) so that they'll grow strong.
There's a lot of "doing" associated with a greenhouse--and with gardening. Our challenge is to simply "be" in the garden with as much mindfulness as we can muster.
Sometimes the "being" is simply "being with doing." Simply being with a young May garden requires a lot of our attention.