Hmmm.  Just another thought.  Perhaps the duration of time is not a good test of a relationships goodness, but how about "the taking of time".

The taking of time to listen, to open doors, to help fold laundry, to cut the lawn, to fix the car, and/or to give a butt brush in the kitchen while cooking dinner.  Over the past many months, I've been thinking about time and its being the most valuable, finite resourse of mine.  And if I use something that is more valuable than all of my money on the one that I love, then that action - that *spending* of my time should speak volumes of my view of our relationship.

And I bet that could be measured and a positive correlation could be made between those time-acts and a relationships goodness.