The action must start in 28 days.
They must announce 7 days before so must be announced by Friday fortnight (21days from ballot)
The protected period starts from first strike.
BA will almost certainly say there isnt a protected period as its a continuation of the existing dispute. BA probably wont announce their intentions until after strike dates are announced. Unite may want to take this to court before any strike, so the longer they leave it the greater the risk of the ballot timing out.