I see there were no 777s scheduled this summer, but that's not to say they didn't operate.
Those two 777 flights are scheduled for the day before the beginning of Sukkot until the day after it finishes. It's a reasonably popular time for vacations though it seems strange that they scheduled for that but there isn't the traditional extra capacity for the more important holidays of Rosh Hashanah and Yom Kippur this year.
Unless they add the flights late, which is what I think they did with those two extra flights on the 26th. I only happened to notice them during an idle dummy booking, and I'm sure they weren't there a couple of weeks ago.
Edit: I've just seen what they've done. The 777 on the 27th September is to "make up" for there being not any service at all on the 26th for some reason or other, departing in the middle of the night. There are also various departures on other days at other hideously unsociable hours in the early morning. The Jewish high holidays sure screw up El Al's schedule don't they? I take it LTN takes the brunt of the bad scheduling because 24h and slots.