H-hour is New Year's Eve.

4 seconds sound clip from the Ocean's 11 (1960) movie soundboard.

You can hear this line at 00:54:34 in the Blu-ray version of the movie.

Quote context

[...]

- Lieutenant, I think you and the Sergeant ought to feel pretty proud of yourselves.

- Now you've given us the good news, how about the bad news?

- Sergeant Ocean.

- This is our objective. Las Vegas, Nevada. Mission? To liberate millions of dollars.

- Now these are the five casinos we hit: Sahara, Riviera, Desert Inn, the Sands and the Flamingo.

- H-hour is New Year's Eve.

- Units involved: Special combat teams made up of former members of the 82nd Airborne.

- Just for curiosity, how did you figure this was a job for old paratroopers? Why didn't you just get some regular heist guys?

- For the best of reasons, Mr. Harmon.

- A man with a criminal record can't get near Las Vegas much less the casinos.

- I guess that lets me out.

[...]