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My son had reflux and colic and weight issues so nothing really stuck until like 12 weeks but we kept a 3-hour EASY cycle for feeding purposes and held to a 730pm bedtime and 730am wake time pretty early on - like around 6-8 weeks like you. So basically we always knew to feed him every 3 hours unless there was a growth spurt and he was hungry earlier, and tried our best to get him to not puke and get some sleep. Largely not successful until we got his reflux meds fixed and the colic passed, but after 12 weeks it was pretty much like your schedule. He would have about 70 minutes of wake time first thing that increased about 10 minutes at each subsequent wake time, which meant 3 naps a day and sometimes a 30 minute disco nap if he was tired. He was in bed between 730-8pm and we did a 1030pm dreamfeed. Once he was actually sleeping all the way to 7-730am off the 1030pm dreamfeed we slowly upped daytime ounces in his milk and made the dreamfeed earlier by 30 minute increments. By 5-ish months he was STTN 12 hours and off reflux meds and we've pretty much stuck to that and DS is 19 months!

We put our lo to bed at 7:30 from the beginning. He'd take three 1 1/2 hour naps and sleep 12 hours at night (including waking up to feed though). We also woke him up at 7:30 so that we could have consistent nap times. I know that isn't for everyone, but it worked for us.
There's differing numbers on total sleep needed in 24 hours, but most say 16-18 at that age. So if you're aiming for 12 at night, the rest will be spread out as naps throughout the day. Some babies just have lower sleep needs but I guess I'd aim for the high end first.