Data says the Cardassians are hiding their fleet in the McAllister C-5 Nebula, as it is only 7 light years from the Federation border and 11 light years away from Minos Korva. Jellico then orders the Enterprise to proceed to Minos Korva, where they send a shuttle into the nebula to mine the fleet. However it is acting like Minos Korva and the nebula are right next to each other, the shuttle departs the Enterprise, does its mission, and returns in a very short period. Even at warp 9 it would take almost four days to travel 11 light years, though the type-6 shuttle Riker and LaForge use only has a top speed of warp 4, at that speed it would take almost two months to travel that far.
When Madred tells Picard "the Enterprise is burning in space", he probably uses a figure of speech rather than the literal meaning of "burning".
Jellico orders Worf to prepare 500 antimatter mines to attack the Cardassian ships in the nebula. Later, Riker flies the shuttle with Geordi to place the mines, and there are only about ten of them. Indeed, based on the size of these ten, 500 would be much larger than the entire shuttle.