Expert,
just a quick aside. Agree with previous reply's (particularly Cossack,Mrs Wheely says Hi).
The way we are taught is that you vector to achieve separation then speed control to maintain that separation. Therefore experience of watching green luminous maggots means we have a rough idea of how long that deceleration will take to achieve.
This can , unfortunatley, lead to a "one size fits all" situation, but constant monitoring means we can hopefully adjust flight paths to achieve the desired result.