I bet this gets plenty of answers, how many are correct is another matter.
I believe it to be, not 100% sure but it should be your cruise rate, after all, unexpected head winds against your cruise speed and fuel burn is not the same as holding above a fogged in field, and if fog is expected you should have other plans.
If you eat into reserves holding, you will have more than an hour anyway.
For me and my PVT OPS, I work on 1 hr cruise rate.
Cheers
J
