A-ha. I see. I thought you were describing a whole new structure; I didn't realize that the old log data was still to be used.

Ok, then. That's a great solution. =) Thanks.

The system I derived from the solution you didn't (as it turns out =) provide looks like this at the end of the hour, for users a, b, and c:

2:00 - Previous:  a: 1:00  b: 1:35  c: 1:50
     - Logons:    d: 2:10
     - Logouts:   a: 2:30  d: 2:50
...
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This way, none of the original data needs to be kept. To find out who was logged in at 2:15, you check the Previous and Logons fields against the Logouts field, and anything falling in between matches. It was something like that (minus a couple of nuances) that I thought you meant.
--

Love justice; desire mercy.