I know for a fact that most of the Daggers were dispersed from San Julian back to Tandil prior to the BB1 on 29th April from both the maintenance officer of the Dagger squadron and it's also mentioned in books - so that implies that a possible attack of the Vulcan on the mainland was already being considered BEFORE the first mission was flown. One returned on the 30 April and the remainder at 11.00 local on the 1st May - and then flew missions over the islands, including the attack on the three ships off Port Stanley.