When do babies start entertaining themselves?

My friend Jeff's wife is expecting and told me that they weren't planning to arrange for daycare because his wife (who is a full-time, self-employed sculptor) works from home. Yikes! I had to call Kelly and tell her about this naive thought, so we could chuckle knowingly ;-). We once were that unaware ourselves!! Ah, those blissfully carefree days...

Kelly said she clearly remembers the day when I excitedly called her to tell her that I was doing dishes and *15 whole minutes* had passed before I noticed that Rosalie wasn't demanding my attention and I found her playing alone in her room! Our daughters are 1 year apart and Rosie had just turned two. At the time she was saying, thank god, it really does happen!