It is an unusual expression in Greek. Yes, it could be used but it is not so good Greek. Better "Αύριο είναι μια πιθανή ημερομηνία".
That's makes better sense in English too: ‘Tomorrow is a possible date.’. Otherwise I think that it means ραντεβού.
Does ημερονημία also mean romantic meeting? I searched in two monolingual dictionaries and it wasn't defined that way
Νο, date in the sense of appointment is ραντεβού (romantic, friends etc), or συνάντηση (meeting)
ραντεβού is used for all kinds of appointments έχω ρανντεβού με τον γιατρό μου
Helps to know the origin of the word as well. It comes from the French "Rendez-vouz", so francophones go wild.
The meaning is very close, but I could probably do it tomorrow is called Θα μπορούσα ίσως/πιθανότατα να το κάνω αύριο in Greek.
In Greek language Δυνατός , In English Possible. Kαι Πιθανός In English Probably Oxford Dictionary