"At four o'clock" or without "at"

[Rachel Adams]

Hello.

Can I omit "at" in my sentence?

"See you on Saturday, four o'clock."

[Rover_KE]

Yes.

[emsr2d2]

You can even omit "on" in casual speech. These all work:

See you on Saturday at four o'clock.
See you on Saturday at four.
See you Saturday at four o'clock.
See you Saturday at four.
See you Saturday - four o'clock.

Note the dash in the final example. There would be a clear break between "Saturday" and "four o'clock" when spoken aloud.