Apparently when a variable or function is called but not available, matlab searches network locations on the matlab path and if those connections are no longer accessible, this delay occurs. To confirm that this is what's causing the unbearably long deley, I turned off/on my internet connection(s) and the problem vanished when there wasn't a connection but immediately returned when there was a connection. The link below contains suggestions on how to troubleshoot this issue but doesn't fix it for good.
After dealing with the same problem off and on for years, I wrote a function that fixes it. The function below creates a GUI that lists all network drives that appear in your Matlab history. You can select any (or all) of the drives that you no longer have access to and it will remove those from your history. The effect was immediate for me and I no longer had to deal with the wait time. Other options in the GUI allow you to restore the history from a backup if needed. It's a pretty simple.
If you're interested (and if you're a PC user) please give it a shot and let me know if it works for you, too.