He may be bobbing off and on in the day time due to the solids maybe? They might be filling him up and then not wanting milk - just a guess here! Cutting them back should help.
How long it takes.....wish I knew. Each lo is different and has their own agenda. As for when to feed, look at a 4hr easy schedule. Here is one:
E 7am
Solids 8
S 9-10.30
E 11
S 1-2.30
E 3
S 4:30- 5:00
A (bath) 5.30/6
E 6:30
7 p.m. bed
10.30 Df (if you do this)
This is just a guide of course, so don't worry if it deviates a bit. Remember it's a routine, not a schedule so don't get too hung up on the hours. By going on a 4hr easy you will find that he will eat so much better being just that little bit hungrier. Of course this doesn't solve your original problem, but you might find things improve overall and it will help. If you want to put another small feed at 5 if you still do the tanking up/cluster feeding.
I hope this helps and you all get some better sleep at night.
If you want more examples here is a thread
https://babywhispererforums.com/index.php?topic=10385.0