When you are rerouting do you check your fuel only every 30 min?

Our FPL's have ToC and ToD (with req'd min fuel to complete the flight with FR + ALTN) including for planned step climbs. OM requires a fuel check every 60 mins-if ETOPS and dist between waypoints equates to >60 mins then done ref LAT/LONG vs Elapsed Time. Common sense carries the day once legal obligations met.

PLOG / plan, log

True - would this include a diagram like the Howgozit where with a mere glance you can ascertain your fuel performance throughout most of the flight?

Want to live a long and happy life? - then you have to be " fuel minded". Apart of other important things...
Use every opportunity to check you fuel. Or else you may not be so lucky to find a suitable airport within a gliding range...

- not on the ones I have used, but they do have fuel expected columns from which you can derive surplus/(on a bad day) deficit by simple maths. I have never had cause to use a howgozit for many years with the advent of computer generated PLOGS. Actually, wrong - I did run a hyd quantity howgozit on the back of the docs envelope once when we had a hyd loss rate on an ETOPS flight.