Allow some skew in checking when a router said it was hibernating

Allow some skew in checking when a router said it was hibernating

This solves the problem Roger noted as:
   What if the router has a clock that's 5 minutes off, so it
   publishes a descriptor for 5 minutes in the future, and we test it
   three minutes in. In this edge case, we will continue to advertise
   it as Running for the full 45 minute period.