A Light Minute is a unit of distance, approximately 18 million kilometers (11 million miles), which is the distance light travels in a minute. The range at which ships can engage in combat (i.e. exchange missiles) is typically 4 to 5 light minutes. The Earth to the Sun is over 8 light minutes.
This is a sore point for the scientist under the Andromeda viewership as it raises a few fundamental questions.
For instance how a missile can fly so quickly that it reaches an enemy ship in under a few seconds, it would have to fly faster than light, which is not impossible in the Andromeda universe, however the side effect of FTL travel is that it takes, for an outside observer, a very long time (in case of the Bellerophon thousands of years). Or how a ship can be 'sensed', as the time the information needs to travel back to the Andromeda is so long that the ship would be far away from the spot where it was found by the drones.
A common "sweep" from an Andromeda drone would take months for one stellar system. In the show it takes hours at best.
These factual errors can be dismissed for the sake of the pace of the show, however.