Don't waste breath and stress trying to earn bonuses. Major bug. Even worse when stacking missions "ding, ding, ding, ding, ding, ding" etc. I ignore messages about bonuses. They all go the same way: Get the cargo here sooner and earn a reward but, rush to your destination and on exiting supercruise you will receive the message(s) "we changed our mind, you have zero minutes to deliver" followed a few seconds later by "We thought you were better than that, no bonus for you." Who are these people . . . Darth Vader? ("I am altering the deal . . . pray I don't alter it again.") I have boosted into stations in well under a minute from exiting supercruise and still receive bonus-fail messages even when inside the station even as I am landing on the pad.
The way it should work, and would work in a finished product is that a once a bonus offer is made the goal cannot be changed or rescinded, the bonus amount can not be lowered. Additional bonuses can be offered for even faster delivery but ANY and ALL mission bonuses offered where the conditions of that bonus were met must be paid even if an additional bonus was offered for even faster service which was not earned.
Offering bonuses, then moving the targets, THEN rescinding the bonuses CONSTANTLY, over and over and over is a path towards frustration and rage-quitting.
and all the little message pings are distracting . . .