thanks for the responses.
I would say it's around 24hours before the rash appears. The hairs are quite curly but they are still super short obviously at that time.
I don't think I'm ever going to be the sort of guy who shaves every 24hours. I think I'm more like a once a week type of guy.
I might experiment by close-shaving a patch near the side of my neck and see what happens. The rash is pretty darn ugly so I'm not in a hurry to do the whole lot anytime soon.