(Although IIRC, TNG goofed in Best of Both Worlds pt2 and had the E-D at impulse cross a distance in a timeframe too short to be sublight...)
If they traveled at high sublight, Einstein would come aboard and do his usual party tricks; a trip of, say, three lighthours would probably take 45 minutes or so.
The exact dialogue in the episode says that the Borg have passed Mars and the E-D slows to sublight with "33 minutes, 14 seconds to intercept". We don't know where
the E-D slows to sublight, though, so we don't even have to call in Einstein to "un-goof" that reference. (Mars is somewhere between 0.4 and 2.6 AU from Earth, depending on the orbital positions, thus less than 33 lightminutes away in any case.)
IIRC, E-D was next to Jupiter (or was it Saturn?) when the Borg were just arriving at Earth. I remember when I ran the numbers a long time ago even with the planets closest to each other it would've been FTL...