Check at Bright Angel Lodge Momo: you can prolly hike down to a place called Indian Garden halfway down where the scenery is quite surreal, with glimpses of the Colorado river below you, and hike back up within your six hours.
Me my brer and a friend hiked down, stayed overnight at the national park lodge by the river and hiked back up the next day. (In theory you can do it in a day but definately not advisable cos of the heat-bowl effect). Can you add the extra day? Apparently only 1% of visitors to the GC actually make it down to the river under their own steam. Too many of them burgers methinks...