We started off thinking an hour or two, and ended up spending the whole day. The views from the mansion are wonderful, but don't miss the mansion tour. The line looks long, but it goes pretty fast.
It's worth the stop to also see the grist mill and distillery which are just off the property.
If you own or manage George Washington's Mount Vernon, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.