Just thought i would put my 2cents in.

DD#1 had tummy time and still did not hold head up, sit up or crawl till well over 9 months. She rolle,sat up and crawlled at about 10months all in a week. but did not walk or cruise furntiture till 15 months.

DD#2 no tummy time didn't help with her reflux to un comfy, was rolling at 4 months and started to sit and do the crawl postion at 6 months, put into a hip brace, learnt to roll and sit in this durring that time. Came out of hip brace and crawled within 3 days, and was walking at 12 months with support and on own at 14 months.

Just shows that tummy time is not all it has cracked up to be.