I have a floating row cover set up over one of my raised beds, can I just place a tray of cool crop seedlings (arugula and spinach) under the floating row cover and let them stay there for a few days before planting them out. Or do I need to do a more formal hardening off (bring them in take them out, etc. etc)

(I have been monitoring the night time temps and they don't go below 30 degrees ... if they do I will bring them in).