Tools/Options.../Disable treeview delay

System Default:   Yes

Explorer++ can, if desired, introduce a 500 millisecond delay between selecting a folder in the Folders pane (ie. treeview control) and opening its contents in the Files pane.  This delay is entirely cosmetic; it may prove useful for users who navigate the folder tree using the keyboard.  With the delay, using the up/down arrow keys would not open the folders contents for each folder as the selection was moved up or down.

By default, this option is enabled, disabling the treeview delay; clearing the checkbox enables the delay.