I flew in CW to TLV from LHR on a 777 at a very decent departure time of 0805. I would never want to fly on the a350 if that ghastly 9pm departure is correct. But that is my opinion.
Be aware that the last 30 minutes of the flight we were mandated by Israel security that we had to remain in our seats with seat belts on. NO excuses granted. I would not want to be awakened on a late night flight to be given those instructions multiple times. And yes it was several times that this was mentioned as a mandate.
It is a bit over a 4 hour flight anyway. Very little chance to sleep if you leave at 2100 hours.
By arriving mid afternoon immigration went fairly quickly. Just remember to keep the blue immigration card they give you to exit the country.