Evenly distribute records over months & Year by their review dates

Hi,


I want to distribute 550+ documents over month for the 3 years as the review cycle is triennial, based on their review dates limited to 20 documents per month.
e.g.
Let’s say, there is a document whose Review Date is falling in JAN, 2017 so it counts to 1, and there are around 17 documents their review dates are falling in Feb, 2017 so it counts to 17, and around 11 documents their review dates are falling in Mar, 2017 so it counts to 11.

I’ve to send 20 documents for JAN, 2017. So what I want is to take all 17 from Feb, 2017 and 2 from March, 2017… which counts to 20 in total. How to achieve this condition in unsorted data?

Appreciate your time. Thanks!

ok, so it'll pull out number of days, but what if they are more than 20, I also need to limit them to 20 or the provided limit.