The following tips might help you improve the performance of your application:

Item Shadows

Disable fading item shadows through the ItemSettings.ShadowStyle property. Fading shadows require substantial amount of processing power in order to be calculated and might incur significant loss of performance if you have even medium amount of items in your application.

Optimization

Since version 4.2.1 you can enable item rendering optimization through the use of the Calendar.EnableOptimization property. When this property is enabled, items' visual appearance is cached in an off-screen buffer. When the item needs to be rendered on-screen, the item's contents are retrieved from the back buffer. The back buffer is updated when the item's contents or bounding rectangle are changed. The contents of the back-buffer can also be updated through the use of the Item.OnVisualsChanged method.

Note
Item optimization yields best results when you perform some kind of heavy custom drawing on the items.

Extended Styles

Disable the use of the extended item styles (ItemSettings.UseExtendedStyles). If these styles are enabled, the items' appearance is invalidated each time the mouse hovers over or leaves an item.

Timetable Collisions

If you don't need collision detection in a Timetable view, you can disable it by setting TimetableSettings.EnableCollisions to Disabled.

Default Item Rendering

If you perform full custom drawing of items, or for some other reason you don't need default item rendering, you can disable it through ItemSettings.EnableDefaultRendering.