Nissan Xterra wouldn't start on first crank (or five) but it now back to normal

Drove 400 miles this weekend, tried to start the Xterra in the morning,
cranked 5 times before the car started.  Drove 50 miles, went into a store
for 10 minutes or so, same performance.  Later, car sat for 3-4 hours and
started as normal.  We drove 400 miles home and stopped for gas, for
dinner, no problems.  What could cause this?  All other engine
performance was normal after the difficult starts.  Could this be "bad gas"
picked up on the highway stops?  Should I replace the filter?