At Six O'clock or on Six O'clock?

Could 6 o'clock be written with a numeral and the word o'clock and be OK, or would it need to be written like this: 6:00 or six o'clock. Thanks! To put special emphasis or exactness on the time, use the number, as in 4 o'clock. To be a bit more formal about things, though, write out the number, as in four o'clock.

How do you write 6 o clock?

It's 6 o'clock. It's 5 past 6. It's six oh five.

Is it 7 o'clock or 7 o clock?

In the modern era, '7 o'clock' is just fine. I'd never consider writing 'seven o'clock'.