Saints’ Aviva Premiership play-off semi-final will be played on Friday, May 16, Premiership Rugby has confirmed.
Jim Mallinder’s men will meet either Leicester Tigers or Bath in the shoot-out for a place in the May 31 Twickenham grand final.
The semi-final will be played at Franklin’s Gardens should Saints claim at least a point against Wasps this weekend.
However, if they slip up and Leicester get a maximum five points at home to Saracens on Saturday, the match will be played at Welford Road.
Premiership Rugby has opted to schedule the game for the Friday to give Saints, and possibly Bath, more rest for the Amlin Challenge Cup final between the teams a week later.
Saracens’ semi-final against Bath, Leicester or Harlequins at Allianz Park will be played on Saturday, May 17 with a 2pm kick-off.
That will give Mark McCall’s men a full week to prepare for their Heineken Cup final clash with Toulon on May 24.
“We are delighted that three of our teams have reached European finals this season and it is important we do all we can when scheduling fixtures to give them as much chance of success as possible,” said Premiership Rugby Chief Executive Mark McCafferty.
“I would like to put on record our thanks for the co-operation of our broadcast partner, BT Sport, in making this decision. They played a key role in this arrangement to back the English clubs in Europe.
“Friday evening has been a big success this season and has produced some great matches. With an Aviva Premiership Rugby final spot now at stake, I’m sure the atmosphere and the occasion will go up another few notches.”