I'd call anything below 1000' (inside 3 miles) as "late". Usually, those calls are explained further, e.g., "Continue approach. One departure before you, expect late landing clearance." Depending on the approach type and weather, I may or may not be able to see the runway to gauge the immediacy of the threat, so I may decide to go around sooner rather than later. If I see the departure airplane rolling, but have not received clearance, I may take it down to 100 or 50'. If it's still turning onto the runway, I may go around at 500 or 200'.