Just how far from a planet or other sizeable body does a ship have to be to initiate the hyperdrive? Game wise is there a set number of maneuvers or something after achieving orbit? I am sure its in there somewhere but I must be missing it.

You're not missing it because it's not there.

Some things are intentionally left blank to allow the GM to dictate details to meet the demands of the adventure and encounters.

Ah, ok so if the bad guys are in pursuit tell the players they have to avoid them for ...oh 5 rounds while the nav computer plots the course and you clear the planets gravity and go. If you tell it different next time, maybe its a larger or smaller planet, effects of a nearby moon or whatever. Gotcha!

If this is relevant, also consider making this something to spend Threat/Advantage from an Astrogation check on. Whoever is trying to plot a course can add or subtract rounds to the time it takes to jump based on their check. Astrogation isn't normally a check that a lot rides on, so having to make one under pressure while the pilot evades pursuers could be a good use of it.