When can we start doing tummy time for young babies?

I didn't know that you can start pretty early and it wasn't easy seeing her struggling on her tummy, but the pediatrician told me that you can start pretty early, like 1 month old for 10 minutes 3 times a day. After one week she was kind of steady. At 2 MONTHS OLD she was already rolling from back to tummy and few days later she began to lift her shoulders and head very steady.