Also, it does take "days" to go from star to nearby star at warp elsewhere in Trek. Go from FTL to STL, and this distance in lightyears will translate to a trip duration in years - and the distance from a star to its not-quite-closest-neighbor does tend to be less than ten lightyears.
Also, "years" is a valid expression for "decades"... Although there would be some poetic harmony in the "days"/"decades" pairing, too.
Basically, the only reason to consider this phrase "proof" for FTL impulse is if one wants to believe in FTL impulse for other reasons in any case. But there just aren't all that many good reasons to do that.