Usually, Time Accounts in HR for Dynamics calculate their values automatically. Still, there are cases where manually triggering a recalculation makes sense - for example, if you manually adjusted Time stamps, and the Time Account, having calculated its value with the "old" Time stamp, still shows the outdated value.

On the off-chance your Time Account shows wrong values, manually triggering a recalculation is recommended as first measure to resolve the issue.
This tutorial shows you how to manually trigger a recalculation of Time Accounts.