Well, I never waited super long periods of time after going off (a year at most), I always rebounded quite a bit faster after getting back on HRT. This year I self-medicated for 6 months of HRT (mid-December through mid-June), then stopped for a month while I got serious and decided to see a therapist and a doctor, and then got onto prescribed HRT at the beginning of August. I'd say breast development is at about 9 months-ish, things like facial fat redistribution is back at about 5 months.
While it might be strange, the thing I noticed most was how fast T wreaked havoc when I went off - many changes reverted in a matter of weeks. Thanks to finally getting serious and accepting myself, I'm never doing that again