What factors influence how long supercruise takes to charge?

Solution 1:

An emergency drop out of supercruise, failing to interdict another ship, or the end of a successful interdiction (for both ships) all cause a long "cool down" period for your FSD. There is an FSD cooldown timer that appears below your fuel gauge and cargo scoop indicator.

Submitting to an interdiction results in a substantially shorter cool down period.

Being within 3km of a ship that has a higher mass lock factor than your own will slow down your supercruise charge rate. The mass lock factor is loosely related to the base mass of the ship, but it's really just a fixed property of each type of ship. I think if there is a large difference the supercruise charge time is slowed down more than if it's a small difference.

The system jump mode of your Frame Shift Drive overcomes that mass lock. That is, jumping into supercruise mode will be blocked by a large ship nearby, but jumping to a nearby system will not be blocked by that large ship.

If you're being interdicted, and can't win the interdiction, it's best to set your throttle to 0 to "submit" to the interdiction, so that your FSD cooldown time is minimized. If the other ship is larger than you, and you're not able to get 3km away from them by the time your FSD cooldown is finished, you can overcome the masslock factor entirely by jumping to another system.

If you do get into supercruise (instead of jumping to another system), it's likely that the ship that interdicted you will be right behind you and will interdict you again. If you jump to another system entirely, they will have to have a wake scanner and take (at least) 10 seconds scanning that wake in order to follow you, which is enough time for you to jump to a third system or to drop out of SC. It's extremely rare for NPCs or players to follow to a second system.

Solution 2:

Mass. The mass of other ships in the vicinity of yours prevent the drive from activating at the same speed. While smaller vessels may only hinder it in small measures a Type-9 or Anaconda pursuing even kilometers away can be enough to turn your frame shift drive's charge time into several minutes rather than a few seconds.