In my day I recall it was something like an approach or two, 45 minutes holding, enough to get to No.1 alternate and a 5% contingency for luck.
Had an interesting one last year in my neck of the woods with my local airport (concrete strip) being IAO, both flights had departed CEB with an Air Philippines Q400 5 minutes behind a Cebu Air ATR72, at IAO there are no navigational aids, no lights, no radar, no fuel and a short runway that I still reckon is questionable in length for a loaded Q400.
The approach procedure is that they fly over the top before circling to land and with no radar they can have only have one A/C doing this at a time so the Q400 was told to hang around for some 10 minutes whilst the ATR72 came in, needing to carry round-trip fuel combined with a short runway the Q400 didn't have sufficient fuel to hold for even 10 minutes and diverted back to CEB, whatever reserves they were required to carry they were planning that same amount of fuel twice, for IAO except that whilst legal they couldn't use it because they needed that fuel for their reserves back to CEB.