Chris, I wait until most of the snow is gone from the trail. Scattered patches in the woods, a bit of monorail left, but that is all. On Mt Cardigan, late April/early May. On more southerly/lower trails, up to a week or two earlier. If you have been keeping tabs on how much snow fell on your mtn, which is easy enough with the weather channel or the like plus a friend or two in the neighborhood or reports here or newenglandtrailconditions.com, you can pretty well guess.
We patrol for blowdowns first, clean drains second, just like you. The period before blackfly season hits, ie mid-May, is very active just doing those chores and noting projects for later in the season on 15 miles of trail...
Yours ay, Craig