There's something in the news suggesting Astrazeneca talking about October as a date for a variant vaccineI’d expect redesign to have started already, though it may need more than one. Either way I think both doses will be complete by the end August, some of those in phase 2 may get already adjusted ones.
If redesigned boosters are needed for those being vaccinated now, I’d guess they will be single shots from November ish. Good thing is we should be capable of running through 30mill shots in a couple of months.