There's been nothing about this on any of the Saints site, but one website today claims the game is set up for a midweek date. The obvious time would be on July 24, between the last game in Ireland and the first friendly in Scotland against Dumbarton. Any later than that and it would be pointless - plus Swansea are away on a pre-season trip of their own.
It will be interesting to see what develops.
Story source: icWales