How long do I need to leave the fencing in before this week goes hard

If your talking about the posts use post Crete instantly

Yes. I don’t know what size timbers you have but I’d dig youre hole. Get the placement somewhat where you want it, add abit off water to the hole and add quarter bag of cement, get a piece of scrap wood and prod the air out the cement, repeat this process until the hole is full with cement. Level off youre post and should set daily quickly.

Yes you can do

Use post Crete and if goes solid within about 10 minutes, it’s really simple to use as well.

Use postcrete and it will be set in 20mins

Dig holes get post to correct height you can attach the fence panel if you want to get the height pretty much spot on Pour water half way pour in post Crete sets solid and as others said with in ten mins just be sure to hold the post level for the first couple of mins

Put the fence in level the post pour water then postcrete it gets hard in a short time

use postcrete sets in no time