5 month old dropping a sleep?

Hi there
Im a second time mum, but can not remember the details about when a baby starts to drop sleeps during the day.
With DS1 he dropped is afternoon sleep and extended his morning sleep (after being a 30 min sleeper) so it was a bit easier to tell when it happened.
With DS2, he usually sleeps 1 hour but Im also finding that the old 4/4:30 sleep is harder to reach, so now I just push him to 6pm (from waking at about 2:30) and whilst its a stretch, its working with our current lifestyle, but no other sleeps are increasing, so currently DS2 is sleeping maybe about 2 and 1/2 hours by day until I can sort out what works for him. He is not a routine baby either, which makes it a bit harder. I put him to sleep when he's tired, rather than by the clock and that can really vary day by day. Yesterday morning his first sleep (from a 7am wake up) was at 11:15, and that was after 2 attempts to have him go to sleep).
Did anyone have a baby that dropped their morning sleep at about this age?
In addition, this baby likes to wake up at 4:13am every morning, lately he goes back to sleep and sleeps through until 6;30 or 7 - depending on how much commotion the toddler makes.
Does anyone remember when that last (or first feed, depending on which baby book you read) feed of the night merges with a proper waking time?