benjamin -

Normally you want to get yeast fermentation going pretty quickly,
to avoid other kinds of spoilage micro-organisms getting established.
The marrow doesn't have a lot of fermentable sugars, so I would be
worried about letting the grated marrow sit for 5 days. It might work
if you are doing something else to discourage bacteria, molds, etc. --
say, by adding a lot of SO2 (sulfites). Even then, 5 days seems too
long to me.

People who make wine from grapes sometimes do a "cold soak" and keep
the crushed grapes and skins soaking at a low temperature before adding
the yeast, which apparently helps extract more color/tannin/flavor from
the skins. But it doesn't seem to me that this would really apply to
marrow wine.

I think I'd be inclined to add the sugar sooner -- I'd be uncomfortable
waiting more than a day or so before giving the yeast a reasonable food
supply (i.e., sugar). That's my two cents.

Doug