My approach is to book airfare when they open up and for our holiday trip to Phoenix I booked it as one ways from SJC to PHX and PHX to SJC and applied LUV Vouchers that were expiring. While I wanted an earlier flight to PHX it was a huge difference.

I am flexible. So be it if we arrive to Sedona at 10 PM and save $400. Our tickets are $160r/t a person for 3 using LUV Vouchers vs $478 r/t for an earlier flight or $220 for our flight.

If an earlier flight opens up at a good fare or if ours goes down I will change it to the lower fare but it has to be enough to warrant lesser milage earning.