Slow initial connection to network resources

A million pardons in advance if this question has already been asked
and answered. I've tried googling for a solution, but odds are I don't
know the proper terminology and am therefore not searching correctly.

Here is what is happening. We have several Windows 2003 Enterprise R2
servers that host file shares and network applications. All network
drives are mapped correctly and are not showing up as disconnected, so
that is not the problem.

Whenever a user on our network attempts to access a network resource,
be it a shared file or an application that retrieves data from the
network, there is a significant (perhaps 10 seconds or more) pause
before it finally responds. Subsequent attempts are near
instantaneous.

Except that's not exactly true. If the user hasn't accessed said
resource for some period of time, then it's back to that same initial
delay. Again, after that delay, future accesses are immediate.

Here is what I think is happening, but I'm not an expert and don't
know the proper terminology. As this is on a domain and access to
resources is controlled by Active Directory ACLs, the first attempt to
access the network resource requires credentials to be sent and
verified. Once the user has validated his/her credentials, the server
"remembers" them for a set length of time, if during which there is no
further activity, those credentials expire.

Is this correct? If so, what is the name for this behavior and what
(if anything) can I do to lengthen the period of time that elapses
before credentials have to be reverified. Or is this a bad idea?

Thank you so much for your assistance.

James Blevins