Speed is related to gravity of nearby objects around you, as for deceleration, just keep speed to a point so it doesn't reach below 8 seconds of arrival time until you are close to the planet, then let it lower to six with a set blue throttle and approach destination?
Yeah, I know all about the blue zone mechanics. That's option C of my original response, which seems to put half the trip time into the last 10% of the distance. Reminds me of the joke about the scientist, the mechanical engineer and the mathematician.
The scientist is doing an experiment in which he puts a beautiful naked woman on a table, and tells the others they can approach the woman, but each second, they can only cover half the distance they traveled in the previous second.
The mathematician snorts derisively and turns to leave, exclaiming "This is ridiculous!"
The engineer says "you go, I'm staying."
"Why?" the mathematician asks, "you can only go half the distance each time, you'll never reach her!"
The engineer grins and says "I'll be close enough for practical application."