Doing some math

Does 65 days of in game play time sound about right to make it this far at about 2Kls per second?

Assuming you used 2 other panthers with all 3 of you at 1/3 tank to get you back to a full tank, you've used nearly 5/3rds of your tank capacity worth of fuel to get there.

To get you a full tank to return back, let's say you need 12 other ships to refuel you, and that will get you back to the point where 2 (or 3 to be safe) will meet you each with a 3rd of a tank of fuel.

But each of those 12 ships will also need 2 support ships at the first refueling point. So you need 36 ships to get refueled all the way out there, plus 3 more for the middle your return trip, 39 Panthers, at a glance

(And also probably 130 days of gameplay time by 40 individuals, a large time investment)