I agree that they are creatures of habit, OR creatures of however we train them to be.
Daisy liked to wake up at 4:00. I would take her to potty, but then I put her in her kennel and let her whine until she went back to sleep, or until 6:00. THat lasted a couple of weeks. Now, knock on wood, she sleeps from about 9:15 or 9:30 is to 6:00 ish. We play hard, and she plays hard with her big sis, Sophie. Now, thankfully, she & Sophie are on the same sleep schedule and the adults are FINALLY sleeping thru the night
It's not easy to listen to them whine, but I do believe it teaches them that 4:00 a.m. is not playtime. Good luck!