Is it correct to say: 'when Sarah gets up on a morning, she may press the snooze button'.
I used this phrase in the context of Sarah waking up any morning, not today (this morning) or tomorrow (in the morning).
I was informed that I should have said: 'when Sarah gets up in the morning, she may press the snooze button'.
I was told that to say 'on a morning' is a colloquialism however several colleagues disagree for a wide variety of reasons.
I would appreciate an expert opinion please.
It is correct to say "in the morning" to refer to the general case (i.e, any unspecified morning): "I usually get up in the morning at six o'clock."
I don't recall ever having heard "on a morning" used in AmE, although, with a modifier ("on a cloudy morning", "on a Sunday morning") it's quite common. This would, however, make it less general than what you have in mind.