I've always gone by my 15 minute rule - if you are trying to get into a new sleep time or whatever, extend the time she goes down by 15 minutes every few days, and she'll adjust to it.

Also - I never try to keep putting the kids down for a nap. If they fight it too much, I give up after 15 minutes... and keep them up for 15 minutes.. and then try again. I think Miss M dropped her 3rd nap at 7 months though, and now naps at 9.30 and around 2pm-ish. Before that though, she was sleeping at around 8.30, 11.30 and around 3.00pm.

She dropped it herself though and wouldn't go to sleep one day until 9.30, so I just kept her up one day until 9.30 and she put herself straight to sleep.