Which of the following is NOT a requirement for a single pilot IFR operation?

In a single pilot IFR operation, the regulatory requirements do not specifically mandate that a pilot must have a minimum of 250 hours of flight time. This is not a universal requirement; what matters more is having specific experience in terms of instrument flight rules and related training.

For single pilot IFR operations, conditions typically focus on the pilot's proficiency in flying under IFR, which may include requirements such as having a valid Pilot Proficiency Check (PPC), a certain number of hours in multi-engine aircraft if applicable, and experience in instrument conditions. These elements are crucial for ensuring that the pilot is competent to operate the aircraft safely under IFR conditions.

Thus, while previous flight experience is important, there isn't a blanket rule that stipulates needing 250 total flight hours for single pilot IFR operations, making that option the one that does not fit the requirements.