I will be watching this as my 5 month old is doing the same thing. wakes up between 6am 7am first sleep is at 9am which he will only sleep 40 minutes, down again at 1pm, again only sleeps for 40 minutes.
The last week i cannot get him to have his 4.30 nap and is really grumpy at 6pm but i want to keep him up till 7pm.