Queries :: Display Date And Time User Log On And Log Off

I would like to make a query that count simultaneous connection.

Here is my tables
Users (ID_User, Name)
Date_logon (Id_on, Date_logon, time_logon, Num_user#)
Date_logoff (Id_logoff, Date_logoff, time_logoff, Num_user#)

Here is a part of a query that display users date and time of log on and log off.

Users Date_logon Time_logon Date_logoff Time_logoff
Utilisateur1 13/05/2015 17:38:42 13/05/2015 18:52:15
Utilisateur2 13/05/2015 17:12:21 13/05/2015 17:30:24
Utilisateur3 13/05/2015 16:59:08 13/05/2015 17:16:06
Utilisateur4 13/05/2015 16:54:14 13/05/2015 18:32:13

Then I put that result in a pivot table in Excel. In line we have time logon by date and in column we have time logoff by date.

Here is the issue : In Excel for the 4 lines above, it counts 2 logon at 4PM and 2 logon at 5PM. We should have 4.