I would agree with the not past 50 hours principle but would not get stressed with a couple over, we often do long trips and of course take into account how many hours are left as part of the flight planning and would have no hesitation bringing the change forward for the convenience of having it done prior to the trip.
Ultimately it is a great indicator of potential problems and gives you a trend of wear and tear so worth the effort and relative small cost to get analysed where ever you choose.
Blackstone Labs as I assume others do give pretty good back on the results.