Not in this sentence. There's a clear distinction between day and date, since a day (mon, tue, wed, etc.) occurs multiple times within a month. In a common conversation, people may use day instead, since I doubt it will confuse anyone, but for this specific sentence only "date" is the correct translation.
"Which date in march" seems strange to me because we already know (more than) half the date. I'd never have said that in English because I think most people mean more than a day when saying "date".
The question is if the Dutch sentence is as strange as the English sentence.
If it is as strange, then "date in march" would be the appropriate translation. If it is the normal way to say it, "day in march" would imo be the appropriate translation because I think it's the normal way to express the concept in English.
Nope, 'datum' is a noun, that only means 'the date' (as in the date of today or any other day). To take someone on a date would be 'uitgaan'. And to describe how old something is is 'dateren' (da-TE-ren).
Deze auto dateert uit 1990 (This car is from 1990). It's a bit posh to say it like that, we also use 'komen uit'. Deze auto komt uit 1990. Or Deze auto werd anno 1990 verkocht. (This car was sold in 1990)
Finding the age of an object (v.): datieren.
The date of an object (n.): Datum
Dating someone (v.): gehen zusammen aus (lit. "to go out together").
A date (n.): Date, Rendezvous
To go on a date (phrase): auf ein Date gehen, e.g. Wir gingen auf ein Date = "we went on a date."
Edit: This is German, not Dutch. I don't know why I thought I was on a German comment at the time...