A day can change everything. One day can start a change of events that can change everything. And everyone.
One day you are just friends. Maybe small flirtation, but mostly you are just good friends. You just enjoy their laughter, their strength, even their mood swings. As long as they are being who they are.
The next day, you are something else. You have felt the change. A subtle change at best, but a change nonetheless. A kiss. A word.
A day can change your relationship just as rapidly as a gentle kiss can when you're supposed to be unconsciousness.