We started a bedtime routine at 10 weeks. Before that it was difficult because there wasn't a pattern to his feeds.
Take the lead from your baby really, some say the earlier the better.
Isaac is settled into his bedtime routine wonderfully now. It's nice to have our evenings back.
Now that he's a little bit older we seemed to have settled into a good daytime routine as well but it's not dictated by time. It's as the Baby Whisperer book states, he'll have a feed, activity and then a sleep. We just go around in that cycle. It works out that he has 3 naps a day at the moment. One in the morning, one in the afternoon and one early evening.
I put him upstairs in his moses basket for a sleep during the daytime now so that he gets a better quality of sleep.