19th August I reckon mate. My understanding is that we are missing qualifying rounds 1, 2 and 3, and go straight in at 'Play off first leg/secong leg'.
http://www.uefa.com/uefa/management/newsid=1478141.html2010/11 UEFA Europa League match calendar
Stage Dates First qualifying round, 1st leg 01/07/10
First qualifying round, 2nd leg 08/07/10
Second qualifying round, 1st leg 15/07/10
Second qualifying round, 2nd leg 22/07/10
Third qualifying round, 1st leg 29/07/10
Third qualifying round, 2nd leg 05/08/10
Play-off, 1st leg 19/08/10
Play-off, 2nd leg 26/08/10
Group stage, Matchday 1 16/09/10
Group stage, Matchday 2 30/09/10
Group stage, Matchday 3 21/10/10
Group stage, Matchday 4 04/11/10
Group stage, Matchday 5 01-02/12/10
Group stage, Matchday 6
15-16/12/10
Round of 32, 1st leg 17/02/11
Round of 32, 2nd leg 24/02/11
Round of 16, 1st leg 10/03/11
Round of 16 2nd leg 17/03/11
Quarter-finals, 1st leg 07/04/11
Quarter-finals, 2nd leg 14/04/11
Semi-finals, 1st leg 28/04/11
Semi-finals, 2nd leg 05/05/11
Final (Lansdowne Road, Dublin) 18/05/11