When planning a penetration-testing effort, clearly expressing the rules surrounding the optimal time of day for test execution is important because:

While violating compliance can be a concern in pen testing, the time of day for execution is primarily about operational impact, not direct compliance violation, unless specifically tied to a compliance window.

Testing can generate noise that might obscure actual threats, but this is a general challenge of pen testing, not specifically tied to the time of day in the same direct operational impact way as disrupting business operations.

Testing undeniably adds to the workload of defensive teams, but this is an expected outcome of a penetration test regardless of the time of day, and proper coordination mitigates this, whereas business impact is directly tied to execution timing.

Penetration testing activities, especially those involving vulnerability scanning or active exploitation, can consume significant network bandwidth, CPU resources, or even temporarily disrupt services. Specifying optimal testing times, often during off-peak hours, minimizes the risk of negatively impacting normal business operations, customer access to services, and network stability.