Final answer:
A flight plan delay can occur if an IFR clearance is required less than 30 minutes after filing.
Step-by-step explanation:
In aviation, a flight plan delay can occur if an IFR clearance is required less than 30 minutes after filing.
An IFR clearance means that the pilot is requesting to fly using Instrument Flight Rules, which requires them to rely on instruments for navigation and to maintain a certain flight altitude and route.
If an IFR clearance is needed urgently, it may take time for air traffic control to process and approve the flight plan, resulting in a delay.