Hello t1n5l3y, and welcome to Seven Forums.
It may depend on what menu is being expanded. For example, if you have your HDD's set to turn off after X amount of minutes of being idle, then it may take a moment to expand and populate a menu that includes a item from the HDD that is turned off until the HDD spins back up.
You might see if using the tutorial below may be able to help though. Menu Show Delay Time
Hope this helps,