This doubt came up during a recent exchange I had at work.
The context was the release of some new software.
In the communication to the users, we wrote "[...] will be updated during the night of Feb 21st.".
I was interpreting that as 'the night between the 21st and 22nd', so some time between 8:01 pm on Feb 21st and 5:59 am on Feb 22nd (why these times? See https://ell.stackexchange.com/a/8977), whereas my colleague meant 'the night between the 20th and 21st'.
Thinking about it, there are more 'night hours' of the 21st in my colleague's interpretation, but in my perception 'the night of' a given day could not start the day before.
Unless one assumes that the night of a given day starts at 00:00.
How would a native English speaker interpret that sentence? 20-21 or 21-22? Or is it an ambiguous expression in the first place, and perhaps should one use the more explicit 'during the night between ...'?