It turns out that this is quite straightforward to do in a custom report.
It needs one simple new custom statistic to display the start time of a session.
The report is going to be in the Holdem Cash Player Statistics section so that you can view the stats that you want, so the new stat needs to be in that section too.
Create a new Column called "date_session_start" with the Expression:
holdem_table_session_summary.date_start
Enable the "Group By" option and set the Summary Type to 'Count Unique'. 'Group By' means that all hands for which the session started at the same time will be grouped together into a single row in the report.
Click 'Save'.
Now create a new Statistic called "Session Start" with the name of the new column in the Value Expression:
date_session_start
On the Format tab set the Title ("Session Start") and Width (120). You can leave the Format Expression blank but set the Format Summary Expression field to:
format( '{1} sessions', date_session_start )
On the Categories tab select just Time Played.
Click 'Save' and 'Apply' to create the stat.
(For examples and walkthroughs of this process please see the
Custom Statistics and Reports FAQ.)
Now on the Cash Games > Reports tab select the 'Holdem Cash Player Statistics' section and click New to create a new report.
Give it a name ("Session Stats", maybe).
Add the new "Session Start" stat along with any other stats you'd like to see - Limit, Hands, VP$IP, PRF, etc.
You might want to add a date filter if you have played a lot of sessions so that the report isn't too big.
Run your report and you should see one row for each session displaying the stats.
I have attached my report here and I'll upload it to the
Repository too - this will include the new "Session Start" stat described above.