Synchronise intervall for Facebook for HTC Sense
Al's right, you can't change the sync frequency for Facebook beyond what they provide.

Edit: The below only applies to the regular Facebook app.

But also, all that Facebook syncs is your contacts (and possibly events to the calendar).  It doesn't sync news feed items or notifications, those are only loaded when you actually open the app.  So unless your Facebook friends list changes more often than every hour, syncing more often would be useless.