A session in something else, at least in the .net vision :).
So you want to know what websites are accesed in a particulat time interval. This translates to knowing what addresses are accesed in the specified time interval by a list of interfaces.
The only way to achive this that I can think of is to attach to all the network interfaces and peek at the network communication interceptiong the tcp/ip packages and checking the address of the destionation. Starting with the address you could obtain the domain name.
See articles like this one
Network Sniffer[
^].