When using the start menu the you will notice a delay between different tiers of the menu hierarchy. For the fastest computer experience possible I recommend changing this value to zero. This will allow the different tiers to appear instantly.

follow this step :

1. click Start – RUn – Regedit.
2. Navigate to HKEY_CURRENT_USER\ControlPanel\Desktop Select MenuShowDelay from the list on the right. Right on it and select Modify. Change the value to 0.
3. Reboot your computer.