A/at night

[moseen]

Should I use "a" or "at" and why, please?

He sleeps seven hours a/at night

 

[Charlie Bernstein]

They're both grammatical, and they mean the same thing.

But neither is natural. Try "seven hours every night."

 

[emsr2d2]

"a night" is perfectly natural in BrE.

He works [for] nine hours a day.
He sleeps [for] seven hours a night.

 

[GoesStation]

"a night" is perfectly natural in BrE.

And in American English.