You don’t have to respect both constraints. If you are under radar control, ATC is doing the separation for you. Forget about the time. The time constraint is more conservative and would be problematic in some very busy airports.
During the approach it’s the same: ATC is responsible of the minimum separation. Of course you should adjust your deceleration smartly accordingly if you see you are getting too close to the traffic ahead of you. If you don’t ATC will ask you minimum speed or give you a speed constraint as required to keep the minimum separation.
Standard minimum separation between medium behind a medium is 3nm and can be reduced down to 2.5nm in some airports.
Last edited by pineteam; 24th March 2018 at 14:44.
Reason: Typo.