That, of course, depends on how fast you can hike and climb.
Crabtree Meadow is considerably lower than Mt Whitney: 4,000 vertical feet! If you hike that in 5 hours, you should try to hit the summit by noon. ..so you're still going to need a fairly early start!
Of course, if you hit it during a time of clear weather, without and T-storm activity, then you could leave a few hours later.
