The ground speed should be taken for exit delay coz: 1 If you have strong upper wind than you probably have significant wind shift at some altitude 2 If you have strong upper wind and therefore low ground speed you can afford more time for more separation (and safety) and still be in a good spot
Line of Flight Explained
in General
1 If you have strong upper wind than you probably have significant wind shift at some altitude
2 If you have strong upper wind and therefore low ground speed you can afford more time for more separation (and safety) and still be in a good spot