Sir Gervase returned on August 31, and as of the day of the capture had spent his time with Margaret "for a week now" [Chapter VII], which seems to date the capture to September 7.  But this is impossibly early; the ships of the Armada that made it to Ireland, as Don Pedro's did, did so at about this time, and would have been wrecked near Cornwall much later.

The storm that wrecked Don Pedro's ship was almost certainly that of September 25 (and we know from Chapter VI that the storm was "last night").  No doubt 26 days of wooing seemed like just a short week to the happy lover.