Averaging inconsistent time-stamped data

Greetings!

First, this forum is immensely helpful, thanks to all of those who contribute!

Second, and the reason I'm here, I have a spreadsheet with two columns. The first column is time-stamp data and the second is a mass measurement that was recorded at that time step (i.e. mass changes over time). Normally this would not be too bad of a problem by just averaging every 15 cells, except that the scale we used to log data does not record at constant intervals. Sometimes it will record after one minute sometimes after two, sometimes after ten...

I'd like to condense these measurements into a table that would compute an average of mass measurements for every fifteen minute window. I'm sure this problem goes way beyond what can be accomplished with the AVERAGEIFS function, but sadly that's about the apex of my excel skills. Please see attached image for visual description.

Thanks in advance!

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Click GO ADVANCED and use the paperclip icon to post up a copy of your sample workbook. AVERAGEIFS() can do this, you just need to keep adding parameters.

Like so...:

If that takes care of your original query, please select Thread Tools from the menu above and mark the thread as solved. Thanks.