Would absolutely love an extension for the anniversary event so I (and I’m sure many others) could continue with the Guest Relations Chapter achievements! I started these late and some of them require multiple days to complete.
Anyone else in this position and would love a bit of extra time?
Pretty please WoW team!? 
If you mean the secrets stuff, that is indeed extended / accessible after the event is over:
As far as I am aware, only the vendors and collectibles via bronze and tw badges are going away.
I knocked out all the secrets stuff last night though. It didn’t take that long if thats what you are worried about.
The fel cycle though, that is an entirely different beast 
FWIW the guest relations quest line (which as I understand it is going away, unlike the crate achievements) didn’t appear to have any time gating at all when I did it over the weekend. Depending on how far along you are you can still finish before the event ends.
Fortunately I have the Felcycle! I’m trying to complete the 2 achievements below related to the Guest Relations questlines:
If you use wowhead. You are looking at maybe 2 hours max.
“I saved the party” I only had part 1 complete and knocked out 2, 3, 4 last night in one sitting.
Currently working on it! 
Still might be out of luck for Photo Op! though
Ugh yea… that might you might be SOL since that was a 3 per week one 