Our youngest (now 3) dropped her naps at 18 months... torture.
Things always change throughout the day, breakfast after she woke which could be a two hour window 7-9am, lunch and tea varied depending on what we were up to (days out etc) so never that rigid!
One thing we have always kept to (and has worked) is bedtime. The time isn't set, latest going upstairs is 7:45pm - bath, picking pyjamas, hair dried and styled, a story (or 5), cuddles, tries for a wee, more cuddles and then bed. Also, once little one was upstairs, there was no coming back downstairs.
Longest it takes is an hour on a bad day, but it's every day, no matter what, the second she goes upstairs, she knows it's bedtime - no confusion and much less stressful. I did find that going upstairs too early caused more stress and took longer. I usually try and time it to at least 1hr 30mins after tea is over or she's bouncing off the walls. So if tea is 5pm, she finishes at 5:30pm after pudding etc, then 7pm is a good time to go up.
Everyone is different, but a set routine (not necessarily time specific) works well for us.
Good luck OP x