Tested the logging this morning, hooked it up to a 12v bench supply and turned it on and off a number of times, of course, as the sleep time is 8 seconds, the resolution is no greater than 8 seconds, but frankly that's more than enough for my purposes.

The CSV file that was created was opened in excel, column width adjusted and the format of the cells containing the calculated time changed from 'general' to 'time', the result is thus:

there was a new session start last night as you can see, this was during a demonstration/explanation.

Of course, using excel you can detect weekday, and filter on start time (AM/PM) to get the data required. once I have got the thing hooked up in the car I will probably run it for a week and see what the data looks like. in the meantime I really need to find out what the plug is called that plugs into the REC(rear electrical console) in the back of the Astra...