Normally, a cash basis taxpayer paying by credit card would get deduction for credit card charge made on December 28... but I think the rules for substantiating charitable contributions mean that if you can't get an acknowledgement that they received in 2017, you can't deduct for 2017.
I don't remember the taxpayers'names, but one sort of sad tax court decision showed up semi-recently where taxpayers definitely gave money to charity but the charity (as I remember it) bungled the documentation. Judge said, hey, sorry... law is clear, you don't get the deduction.