In English we would usually say: on Saturday and Sunday.
Can you therefore say: у суботу і неділю ?
Totally. For example:
I thought that, rather than 'у суботу і у неділю', it should be 'у суботу й у неділю', ie. 'й' rather than 'і', since between two vowels. Is this optional? In general not important whether 'і' or 'й' be used?
У суботу й у неділю is better.
It's not obligatory though, it's a recommendation for melodic speech and beautiful writing.
Ok, that's interesting, thank you for your reply.
Is it also appropriate to say "We did not work on Saturday and Sunday"? If not, what word(s) would need to be added to make that so?
That would be "Ми не працювали ..." (past tense)