The time to switch tasks is always a difficult metric because there must first be an agreement on when the operation starts and ends. We like to say that it starts at a point in a Novos service where it determines that a context switch is required. It ends when a new task gains control of the CPU.
However it is measured, there is no single number. The time to switch contexts from one entity to another depends on the type of entity (e.g., Foreground task or Background task), processor and clock rate and compiler efficiency.