If duration is finite it is returned after it has been scaled using Dilated(TimeSpan). If duration is undefined, it returns the remaining time (if within a `within` block) or the properly dilated default from settings (key "akka.test.single-expect-default"). If duration is infinite, an ArgumentException is thrown.

public TimeSpan RemainingOrDilated(
	Nullable<TimeSpan> duration
)

member RemainingOrDilated : 
        duration : Nullable<TimeSpan> -> TimeSpan