Well, for the most part it adds color and tannins; tannins give it
astringency. Concord is black with color so I don't know whether you
need more time or not. I wouldn't think astringency in a Concord is
needed.

If you liked last years you may want to consider making this in two
stages; one where you pull off some free run early like last year,
another where you leave a portion on the skins. (This assumes you
liked the color last year.) To be honest, Concord is usually made
sweet for a reason, it's not especially well liked as a dry wine due
to its foxiness.

If you only left a small portion on the skins you do have a few
options left even if you hate it. You can fine and filter to remove
some astringency, you could blend some back in to the original batch
or you could add some sugar and vodka to make it into a port style
wine. (I don't know if adding vodka is legal in the US; I do think
you are supposed to get the higher alcohol via fermentation which can
be done too. This is an international newsgroup so...)

The long and short of this is if you like the color I doubt you need
extended skin contact. Concord truly is a wine unto itself, it does
not behave European grapes.

Joe