Paste this into a new question or an answer at dba.stackexchange.com:
<!-- -->
> CREATE TABLE myDtTm (theDateTime datetime);
>
> GO
>
> <pre>
> ✓
> </pre>
<!-- -->
> INSERT INTO myDtTm (theDateTime)
> VALUES ('2012-08-28 12:05 PM')
> ,('2012-08-28 12:08 PM')
> ,('2012-08-28 12:11 PM')
> ,('2012-08-28 12:15 PM')
> ,('2012-08-28 12:20 PM')
> ,('2012-08-28 12:24 PM')
> ,('2012-08-28 12:28 PM')
> ,('2012-08-28 12:32 PM')
> ,('2012-08-28 12:36 PM')
> ,('2012-08-28 12:39 PM')
> ,('2012-08-28 12:42 PM')
> ,('2012-08-28 12:45 PM')
> ,('2012-08-28 4:01 PM')
> ,('2012-08-28 4:05 PM')
> ,('2012-08-28 4:08 PM')
> ,('2012-08-28 4:11 PM')
> ,('2012-08-28 4:14 PM')
> ,('2012-08-28 4:20 PM')
> ,('2012-08-28 4:23 PM')
> ,('2012-08-28 4:28 PM')
> ,('2012-08-28 4:33 PM')
> ,('2012-08-28 4:36 PM')
> ,('2012-08-28 4:40 PM')
> ,('2012-08-28 4:44 PM')
> ,('2012-08-28 4:47 PM')
> ,('2012-08-28 8:01 PM')
> ;
> GO
>
> <pre>
26 rows affected
> </pre>
<!-- -->
> SELECT theDateTime
> ,SUM(TimeDiff) OVER (ORDER BY theDateTime)
> FROM (
> SELECT
> theDateTime
> ,CASE WHEN COALESCE(DATEDIFF(minute, LAG(theDateTime, 1) OVER (ORDER BY theDateTime), theDateTime), 100000) > 10
> THEN 1
> ELSE 0
> END as TimeDiff
> FROM myDtTm
> ) sq
> ORDER BY theDateTime
> ;
> GO
>
> <pre>
> theDateTime | (No column name)
> :------------------ | ---------------:
> 28/08/2012 12:05:00 | 1
> 28/08/2012 12:08:00 | 1
> 28/08/2012 12:11:00 | 1
> 28/08/2012 12:15:00 | 1
> 28/08/2012 12:20:00 | 1
> 28/08/2012 12:24:00 | 1
> 28/08/2012 12:28:00 | 1
> 28/08/2012 12:32:00 | 1
> 28/08/2012 12:36:00 | 1
> 28/08/2012 12:39:00 | 1
> 28/08/2012 12:42:00 | 1
> 28/08/2012 12:45:00 | 1
> 28/08/2012 16:01:00 | 2
> 28/08/2012 16:05:00 | 2
> 28/08/2012 16:08:00 | 2
> 28/08/2012 16:11:00 | 2
> 28/08/2012 16:14:00 | 2
> 28/08/2012 16:20:00 | 2
> 28/08/2012 16:23:00 | 2
> 28/08/2012 16:28:00 | 2
> 28/08/2012 16:33:00 | 2
> 28/08/2012 16:36:00 | 2
> 28/08/2012 16:40:00 | 2
> 28/08/2012 16:44:00 | 2
> 28/08/2012 16:47:00 | 2
> 28/08/2012 20:01:00 | 3
> </pre>
*db<>fiddle [here](https://dbfiddle.uk/?rdbms=sqlserver_2014&fiddle=920b573556afc279224880faac4562a0)*
back to fiddle