Question about elapsed time

I have dataset consists of 2 columns named Dateandtime and magnitude as follow

6/11/2015 9:19      5
6/11/2015 16:12      4.8
6/11/2015 18:46      4.9
6/11/2015 19:37      4.4
6/12/2015 5:57      4.5
6/12/2015 6:57      4.5
6/12/2015 18:29      5.3

i want to find elapsed time for 10 days time period then next ten days and so on.... dateandtime column are of cell type. Kindly need help for this... Thanks in advance

[Martin Schätz]

Hi, can you post some example of your code? What did you try? Are the dates numerical or string?

[Walter Roberson]

Is "elapsed time" the time of the last entry in the 10 day block minus the time of the first entry in the 10 day block?