here günlerden is not necessary but used to make it clear and put emphasis. günlerden literally means from the days so you let us know that you talk about days at first hand.
it's exactly like -> It's year 2015.
Of all days, it is Friday. Another similar structure we use sometimes: "the month of May"
although it sounds grammatically correct we don't use it that way. it sounds awkward or too colloquial. prefer yarın günlerden cuma or yarın cuma
A lot of people say cuma günü. Yarın cuma is probably the most common. I would say günlerden is not used too often in this context.
It's like (from the -) in English, ex: Okuldan = from the school.
but it is not necessary to have the same meaning of what I explained