This depends on what area of the system you are referring to as each feature works differently and for good reason.
Dashboards: These refresh on an hourly timer.
Project Schedule and Task Data: The database is updated as soon as someone commits a Save to the schedule. However, the schedule does not auto-refresh on its own, unless you make a Save. So if you have a process when multiple users have the same schedule open for editing, then use the Refresh button at the top of the schedule screen to be sure you have the latest schedule.
Nightly System Recalculation: For financial, newly entered company holidays, and auto-pushing of schedule dates, this occurs once every night.