Your math IS lousy :D
64 manufacturer`s GigaBytes = 59,6 real GigaBytes
59,6 GBytes = 476,8 Gbits
476,8 Gbits capacity / 12 Mbits per second bitrate = 39 733 seconds = 11,04 hours
Edit: when in parking mode, Blackvue doesn`t record continously, but only when motion is detected.