Half marathon - 3 week taper too long?

[RandomMcRandomface]

Interested in advice - I am thinking of training for a half in May. Problem is I know I won't be able to do any significant training the three weeks beforehand so would effectively have to bring my training forward and taper for 3 weeks. Is this too long for a taper?

I can run 10km now but still need to build up to 21.

I did a 3 week taper for London marathon a few years ago and it massively paid off. I would do a final long run of 18k as close as possible (i.e. right before you start tapering) and then just really try to do 2 x 5-10k as a minimum for the first week of the 3, and then maybe 2 x 5k, and 2 x 3k.

I'm encouraged to read this, 11 days ago I ran 10 miles and the next day my left foot was very painful (it was a pain I've recognized before so I'm guessing same injury flare up) but I'm concerned as I'm doing my first half in 3 weeks time (hopefully). My trainer says with all the miles I've put in in training, having 2/3 weeks off then doing the half shouldn't be a problem but I'm getting a bit anxious tbh! I've got a physio appointment on thurs so will see what they say and then plan from then I guess. Does that sound okay?