Bubble of Faster Time for FTL
So in a setting I've been making, I was initially going to use Alcuberrie drives in an attempt to at least have it be "aldente scifi," at least where human technology was concerned. But further reading basically said that the math doesn't math out for that in terms of actually using them. So I looked into other options. I saw Krasnikov Tubes and they are cool; I included them as Earth's first attempt at interstellar travel, but they introduce some weirdness to the setting that idk if I can or want to deal with. I never liked straight hyperdrives, but I did get an interesting idea.
What about a bubble around the ship, in which time is accelerated? Say you want to travel to Alpha Centauri, 4.2 light years away. If you can accelerate to a huge fraction of the speed of light, say 0.9999c, that trip will still take you about 4-and-a-bit years. But what if you could experience those 4-and-a-bit years at twice the speed, like reverse time dilation? An outside observer sees you make the trip in 2 years, but your ship still experiences the full 4 years.
"Isn't that still faster than light travel?" you ask. I say no, not any more than seeing the dot of a laser pointer moving from the moon to the ground seemingly faster than the speed of light when someone flicks it. The ship is moving at relativistic speeds, yes, but not super liminal. The field is being projected around it either at the speed of light or just slightly faster than the ship so it doesn't overtake it's own field. The bubble itself appears to move faster than light perhaps, but only because it is being propagated through a faster time-frame.
I tried searching for this and everything just linked back to the Alcuberrie drive, probably because of the word "bubble," even though I think this is very slightly technically different. Are there any examples of this kind of inverse time dilation, or am I just describing a warp drive in a roundabout way?
And yes, I know that there is no evidence in modern day for "reversed time dilation" and something like it would probably require negative mass density.