You can book sny Hilton family of hotels directly with your points by calling the HGVC center (not Hilton reservations). However, your point-cost for doing so is quite high. Its like converting your HGVC points to HHonors at a ratio of 1:20, meaning that, if the hotel room would go for 40K HHonors points per night, they will charge you 2000 HGVC/night.
You can also convert any of your next year's point-alotment to HHonors at a slightly better rate of 1:25, but they will not post to your HHonors account until next January.
Either way, it's far better to book a studio at a HGVC resort, if at all possible.
You cannot use Open Season rates for hotel stays. That's only for booking unused HGVC units at the "last minute."