In the part of the “Animations” tab reserved to the main menu there are three options: effect, use reverse effect and duration.

Main menu configuration
From the “Effect” parameter you can choose an effect from the drop-down list in order to set-up how the effect will animate on rollover.
The second parameter here, “Use reverse effect”, adds a reversed effect on rollout, if enabled.
From the other parameter present here you can set-up the duration of the effects; the value you insert in this text field is expressed in frames (thirty frames are the equivalent of one second).