Expression and Where?

[Jay]

Thank you in advance.

Here is my table using DateDiff().
User Action ActionTime FirsttLogOn LastLogOff LogOnDiff LogOffDiff
User1 Logon 10:04:24 10:00 19:00 04:24 -6:53:36
User1 Logoff 18:56:44 10:00 19:00 8:56:44 -3:16
User1 Logon 13:23:34 10:00 19:00 3:23:34 -5:36:25
User2 Logon 11:07:04 11:00 20:00 07:04 -7:52:56
User2 Logon 15:34:23 11:00 20:00 6:34:23 -4:25:37
User2 Logoff 19:52:34 11:00 20:00 7:52:34 -07:26

I want to filter only 1st and 3rd rows. Filter is based on that for each
user (Action = Logon) and (LogOnDiff is smallest positive Number).

And at the same table(query) want to add only 2nd and 6th rows. Filter is
based on that for each user (Action = Logoff) and (LogOffDiff is smallest
negative Number).
I am new to this area.
Would you please write down the expressions and tell me where I put it in
acess.