I've run into a "higher level" editor that disabled PM's. I ran into this because they have locked segments that were causing wazer's to submit problem reports.
So getting back to the original etiquette question... I usually send a PM requesting a response within 24 hours for level's 3 and lower and 48 hours for levels 4 and higher. (simply because I'm a 3 and can deal with the "lower" stuff.).
If I don't hear back in the time frame I either fix it myself, or I submit an unlock request in the forum, usually stating why I need it unlocked. Yes there is more "administrative overhead" (more work on my part to keep track), however, I find that a notepad doc on my desktop works for the little stuff just fine. For bigger issues I update my To-Do page in the wiki for my area (major issues).
Hope that helps! (IMHO, a simple button in the left side of the map editor that shows up when a segment has been edited by someone withing the last XX days or something. That button could be configured to allow you to type a short note, and in the background sends the user responsible a PM with your note, a permalink to the segment, etc.)