Straffles I don't think they necessarily remain exactly the same, but pretty close, and the kid gets more flexible as they get older. By the time my son was 18 months old we pretty much had a set nap of 12.30, because that worked with lunch. By the time he was 2, if he occasionally (OCCASIONALLY) missed his nap, it wasn't the end of the world, though most days he would still sleep 2hrs+. 1 nap didn't solve EWs for him, he was always the king of EWs and nothing solved that until he was 2.
Aishi, I don't think I've ever really managed to get her down much before 6. Thankfully she's not really an EWer, OT tends to be more NWs than EWs with her.