I never stressed over "tummy time" per se. Personally, I think setting a "minimum" that each individual child should get isn't ideal - but more of a way of giving information to mothers who otherwise might not understand that their child needs an opportunity for free, unrestricted movement in a variety of positions. Since the "back to sleep" campaign is so prevalent, babies usually get plenty of "back time" for movement, either movement in their sleep or upon waking before a caretaker is there to get them. DD was not a big fan of "tummy time" until she got old enough to actually hold her head up for longer periods, because it otherwise limited her perspective. So I just made certain to play with her during floor time in many positions while giving her enough space that she had unrestricted movement. FWIW, she wasn't a back-sleeper, either. From a very early age, around 6 weeks, she was able to get onto her side on her own most of the time, and if she was laid on her back to sleep, would generally end up in this position anyway. A couple of weeks later, she would awaken if laid on her back to sleep and we began placing her down on her side to sleep - she would stay on her side all night long in most cases. By 2 months she could roll on her own and slept in a variety of positions of her own choosing - mostly either her side or tummy. I didn't stress over this, either - I'm not going to constantly risk waking a well-sleeping baby in the night to flip them from tummy to back when they've gotten to their tummy on their own.