As long as the safe harbor minimum is satisfied by tax withholding alone, then extra Quarterly estimated payments aren't considered as to when they were made....they just go in as an additional credit against taxes owed.
Depending on which of the safe harbors you are referring to, make sure you re-read them. Current year safe harbor of 90% of the final 2019 tax assessed is pretty straightforward. For this one you really need to have an accurate idea/guess or overestimate of what that tax will be...and if you hold significant Mutual Fund investments...that can be all over the place since you won't know what they are spitting out as year-end cap gains, or interest and dividends until December (usually).
....but the prior-year safe harbor has a subtilty... either, that you paid in more than 100% of last year's total tax assessed as long as your AGI for 2018 was less than $150,000 ($75,000 if MFS ). But if the 2018 AGI was higher than those amounts, then the 2019 tax pre-payment must be at least 110% of the 2018 assessed tax.
And, of course, the IRS can change them, usually to be more lenient....like they did so at the last minute for 2018 tax returns. ( I find that somewhat unlikely for 2019, but then politics/congress might intervene )
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(Not sure exactly what CCD minimums you are referring to...but I'm guessing you have a type of credit card that needs some minimum use to avoid other fees...or something of that sort)
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
