This is great information! This tells me that earliar bed WILL work (you got 11 and 10 hours when you tried), but that he still isn't in bed soon enough, hence the long time to fall asleep, NWs and still iffy sleep. Notice that when you moved bedtime forward from 6:45 to 7:15, you got 1 whole hour LESS of sleep. The 40 minutes may go down if you go even earlier than you just did. I know that may seem scary, but my son has had 5:45 pm bedtimes before in an effort to battle the OT regime we were in!
The thing to remember is that this really early bedtime is NOT permanent: it's merely a measure to get us thru this OT cycle, and get him the better sleep he needs to help him not be so wound up at bedtime. Also, it typically takes 3 nights of a change before their body responds 100%. So, the fact that you had initial success of him sleeping longer is extremely encouraging! The 2nd night you already slipped by 30 minutes later in bedtime, and had less sleep as a result. 30 minutes is a ton when you are dealing wiht an OT cycle.
The waking at 5 is a product of being OT as well, so while it is very frustrating now to have him wanting milk that early, it is temporary until we get enough sleep in the little guy. What I would be tempted to do is give him a sippy cup with milk, and tell him "It is not time to get up yet. Drink your milk, and when you hear mommy's alarm go off, then it is time to get up." Set your alarm for 6 am, and then go get him up for the day at that point. IF he fusses, you go in and remind him "It isn't morning time yet. Mommy's alarm will ring when it is time to get up." Of course, if he falls asleep after the milk, that's great! Turn off your alarm and try to get some shut eye! But I'm thinking he won't sleep until AFTER we get a few more nights of better sleep under his belt.
New plan: start bedtime routine at 6 and see where that gets you. Be super strict about that! Treat it as an experiment, and note any changes in sleep that happen. Keep this up for 3 nights before deciding it's not working. But I have a feeling after 3 nights you might see some definite improvements. I know you saw some NWs with the earlier bedtime, but that is because he is starting to get closer to the right amt of sleep. Those NWs will disappear once we kill this OT cycle. That will just take a few nights of getting 11+ hours of sleep.
This stuff is SO tough! Sleep deprivation is hard for kid and mommy. It *will* get better -we'll work it thru.