I have a multi-row, multi column spreadsheet. Of the columns, 3 of them are
the most crucial. Let's say,

Column A is: User
Column B is: Date
Column C is: Cycle Time (Calculated from B and another column)

What I would like to know is the average (median, etc...) Cycle Time for
the FIRST 25% (50%, 75% etc...) of the Users signed up.

Any ideas?