Factual error: Master Sergeant Alexander "Al" Apone U.S.M.C. ranking was wrong on his uniform. His uniform showed a U.S. Army Sergeant First Class rank. (You can see this when they were loading up on their APC.) The correct ranking should have been 3 chevrons up, crossed rifles in the middle, and 3 rockers on the bottom. *Yes, in the future, the ranking system could have changed.*
Revealing mistake: When Ripley enters the elevator to go down into the hive, her pulse rifle/flamethrower combo is a stunt prop. The giveaway is the pulse rifle's front is blank (literally just a flat surface with no detail and no holes for the barrel or the grenade launcher). It's particularly obvious in the newer HD versions.
Answer: The company doesn't wait 57 years, they built a colony on the planet over 20 years prior to finding Ripley. The company was apparently unaware of the exact location of the derelict spacecraft. After finding Ripley and obtaining information from her, Burke was able to send the Jorden family to the precise location of the derelict spacecraft.