Going somewhat OT.
A few years ago I went to Easter Island - 767 both ways and had a similar question. I was able to talk to one of the flight crew and although his English wasn't good (and my Spanish is non-existent) I understood that, for a start the flight time can vary from 4 to 5.5 hours. With no alternate the way it works is that they have a point beyond which they cannot go unless (1) the weather is confirmed as "OK" and (2) the departing aircraft has left. The 2nd one intrigued me but when we arrived I began to understand. The runway is both wide and long. I gather the US paid to extend it as an emergency point for the Space Shuttle. However, the stand space is miniscule. Basically 2 stands plus a stand where they can store one more aircraft which had a TUI 757 in it on some kind of RTW air cruise although looking at Google maps it seems to be just 2 stands
https://www.google.co.uk/maps/place/...4d-109.3496865
My point is that an alternate isn't always in the immediate vicinity of your destination and can be behind you.