How can I reduce the LAN communication time when using the E5810A to connect directly with my instrument?

By default, VISA searches the network (LAN connection) for a hostname. After a period of time, when a host is not found, VISA then looks for any instruments that may be connected.  You can provide VISA with the specific instrument information so that it is located immediately and bypasses the network search time.
In Windows (NT, 2000) locate and open the file 'hosts' using Notepad at the following location:

C:\winnt\system32\drivers\etc\hosts

The file should look similar to this:

As shown above, add an entry that looks like this:

169.254.58.10 E5810A

Where the IP address is the address of your E5810A.

The entry should be added before the localhost entry.