DMIN Function

you don't say if date and time are in the same column or different columns? is it 9/30/2018 6:12:31 in the same cell or is it 9/30/2018 in one column and 6:12:31 in the next column?
the answer can make a difference as to what formula you are given.

I took a guess and with the understanding the times are in a different column than dates ...

In the attached I copied the bins into column F, removed duplicates.

Then in G2 array entered this formula filled down and across.

If you aren’t familiar with array-entered formulas array enter means the formula must be committed from edit mode by simultaneously pressing and holding down Ctrl and Shift while hitting Enter.

Formula:

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and reformatted for date / time / General

If I understand the initial layout, modeled in columns A:C, then you could populate Dave's date and time columns respectively using: =INT(B2) and =MOD(B2,1)
Let us know if you have any questions.

It appears that the values in column A are derived using the FLOOR or FLOOR.MATH function and are already grouping times into two minute intervals. Could you supply an example of what you are attempting to accomplish and how what you are doing now is not working?