I agree with Dojo. This is the way we have been using it for some time. We've used 'READY - READY - HACK' call and on the word 'HACK' all pilots would then press the HCK key on the UFC to initiate the count down timer. This way it doesn't matter how long the pilot need to punch in the time.

However I just did some test just now (in 1.5.2. and 2.0.1) I couldn't really get it to work as I thought I used to. Previously I have only used it on e.g. a set of coordinates given by JTAC and there is works nicely. For the flying a flight plan I could get any good result.

From the initial trial it seem like the HACK entry isn't linked to the current steer point shown in the HUD, but more linked to waypoint page shown in the CDU.

This is a little inconvinient as you then cannot simply look at the HUD but have to get heads down but it might be the way it is in the real jet.