How long is a piece of string?
It all depends on how fast you want to transition. Assuming Contra-Grav, One G-Turn of burn will get you to 1g velocity. You could coast out to the 100-D limmit and jump just on that. Arrival in the next system retains momentum however depending on Astrogation task roll degree of success you might be pointing the wrong way. At only 1g velocity you'd only need two more G-Turns of burn to get you heading inbound.
So the minimum would be, to allow a saftey margin, 3 G-hours (6 G-Turns)
That is the slowest, allows very limmited magin for error, virtually no option for Gas Giant skimming, and definately no combat.
I preferred to build ship designs with ATLEAST 40 G-Turns, so 20 G-Hours.
Most of the published ships ranged from a low of about 36 G-Turns for the yatch, to a respectable 73 or so G-Turns, from memory, for the Liner.
