Anytime between 6 and 10 months :) even if he's on his back, you can place toys around him within sight to encourage him to roll and move. I didn't do much tummy time with my baby but notice he gets encouraged to do it himself when his toys are within reach. https://sg.theasianparent.com/baby-crawling-a-guide-for-mums-and-dads
Hi, The baby should crawling anytime between 8 to 10 months. To make it fun and encouraging - you can place toys randomly around your baby which will motivate him to roll and move to reach to the toy :)
same. my 8.5 monrh baby hates tummy time and not crawling