How is the endurance 3h 8m calculated? No time is given for the contingency fuel, but clearly it contributed to the endurance. At the fuel flow for the chosen power setting (31.7 l/h), the contingency fuel would contribute 14 minutes for a total of 2h 17m+45m+14m = 3h 16m – 8 minutes more than the total computed by SkyDemon. (The times for enroute and holding are correct.)

Am I missing something or is there an error in how SkyDemon computes the endurance? (If there is an issue with SD, now would seem a good time to address it as the fuel plan calculations are about to be reworked anyway to include Final Reserve Fuel.)

That would indeed be what you expect. But, the contingency fuel / fuel burn in cruise is 7.4/31.7 * 60 = 14 minutes.

Enroute + holding + contingency would be 2h17m+45m+14m = 3h16m.

If the cruise fuel flow is used for the holding fuel, then it would be 2h17m+35m+14m = 3h6m

However I try, I can't make out where the 3h8m comes from.