After a few days, it's natural for the call UI to be swapped out.

I've had uptimes of over a week with heavy use, and at worst it takes 3 seconds for the ringer to start (Vibration starts first, then the screen unlocks, then the phone is brought up with the ringtone)

Check your Maemo installation for things that may affect performance (daemons, services, plugins, etc) and disable the ones you don't need, or don't use often.