Geez, I said I'm not discussing the scenario with 747 going around against cessna departing, the bit with 747 outclimbing the cessna was only a joke...
ICAO DOC 4444 5.7.1. says:
1. If the arriving a/c makes a full instrument approach, a departure can be released:
a) In any direction up to the point when the arriving a/c commences procedure or base turn
b) In direction differing by at least 45 deg from the direction opposite to final, if the arriving a/c has more than 3 minutes to the threshold
2. If the arriving a/c makes a straight-in approach, a departure can be released:
a) In any direction - at least 5 minutes before the arriving a/c reaches the threshold
b) In direction differing by at least 45 deg from the direction opposite to final - 3 minutes before the arriving a/c reaches the threshold, or before it passes a designated fix
I don't think it will let you release Lear with cessna on 3 miles - unless you have this fix from point 2b at 2 miles, or cessna is doing 40kts, or you're not applying this rule.