It's become tradition to make rose hip syrup each autumn, I wrote a rough method last year. While out and about each year we try to earmark particular locations for the future gathering of fruits. Our go-to hedge for foraging has a marvellous quantity of several bounties, one of which being roses. Back in spring we gathered rose petals and in early autumn it became time to harvest rose hips. There doesn't seem to be a 'right time' to pick them; they're either solid bullets or already a pulp so just gather any red ones that haven't started to go rotten and be glad there's enough to make a meaningful batch.
I use my hedgerow cookbook recipe as always which this time made 3 bottles' worth; my winter cold avoidance ritual wouldn't be complete without it.

Take care,
Sophie