John-
Sounds like a fun trip- I love that route, one of my favorites. (I may do a similar route for my DV trip, which hopefully will be finalized shortly. Been dealing with a few issues.)
Just thought I should give you a heads-up.
Given your posted itinerary, if you make very short stops, and you (your group) have no mechanical issues, you'll be very lucky to make it to HWY 178 at the end of Warm Springs Canyon by 5 pm, let alone getting to Badwater, Furnace Creek, Stovepipe Wells, sand dunes, etc. Be sure to visit the Talc Mine at Warm Springs. (N35° 58.0539' W116° 55.8137')
Wow, I never thought I'd come across somebody more optimistic than I regarding the timing of a trip.

God knows I like to fit as much in as possible.
My best guess is that you'll be back at Panamint Springs around 8-9 pm.