When is the APU typically shut down following engine start?

The Auxiliary Power Unit (APU) is typically shut down 30 seconds after engine start because this allows time for the engines to stabilize and reach operational parameters necessary for safe flight. During this critical initial period, the APU provides additional electrical and hydraulic power to support systems as the engines come online. Shutting down the APU too early could compromise the aircraft's power and hydraulic needs, while waiting too long can lead to unnecessary fuel consumption and wear on the APU. This timing balances operational efficiency with safety considerations, making it a vital part of standard operating procedures for aircraft ground operations.