The A-Day parade is usually at 10:00 am. We have found that getting through the gate at least two hours before a parade gives us enough time to park and walk (or ride the bus from the parking lot) and find a seat in the bleachers without having to worry and rush.
There is handicapped parking behind the bleachers, or if you do not have a handicapped sticker, then you may drive near the bleachers and drop off your relatives that cannot walk very far. There are good locations for wheelchair visitors to watch the parade, either from the sidewalk on either side of the Plain or in the designated area in the bleachers. Last year the Public Affairs Office answered this question....perhaps they could give you more information about handicapped access.
I think that staying within 30 minutes to an hour away from West Point on Friday night would be preferable to driving up that morning. Cadets really enjoy spending time resting and visiting with their families after the parade. In years past they have let the Plebes go back to their family's rooms after being released on Saturday...so staying within an hour of West Point is nice on Saturday night, too.
Have you joined prospective-net? These questions may be answered more fully there.
Here is a link to a map of West Point...this map may be in the back of one of the candidate appointee booklets.
http://www.westpointaog.org/NetCommunity/Document.Doc?id=592
I have many pleasant memories from A-Day. I know you and your family will enjoy the parade. You are wise to plan ahead!