At the start of Aliens we learn that Ripley has been frozen for 57 years after the events of the first film. When Ripley is asked to accompany the Colonial Marines after contact with colonists on LV-426 is lost, the crew is frozen for the journey. I assume the purpose of freezing the crew is because it's a long journey (years?), so that would make perfect sense. Before they leave we also learn that there have been colonists on LV-426 for 20 years. If contact was lost, how long would it take colonial marine to reach the colonists?
The script for Aliens prefixes the scene with the marine crew waking from hypersleep with:
EXT. DEEP SPACE - THREE WEEKS LATER
So the short answer to the question is three weeks.
So you might ask, why the huge difference (almost 1000x different duration). The difference between the 3 weeks and the 57 years might be explained through multiple reasons:
The escape craft that Ripley takes at the end of Alien may not have anything like the speed of the military ship, especially after 57 years of further development. The Nostromo itself was only a few more months away from Earth when it stopped at LV-426. So even a 'slow tanker' craft was capable of making that journey in less than a year.
However Ripley is surprised how long she's been asleep, so it can't all be relative speed of the vehicles. The main factor is that the escape craft almost drifts undetected through known space before it is picked up and Ripley taken to Earth.
You'd drifted right through the core systems. It's blind luck that deep-salvage team caught you when they...are you all right?