I think you'd be better off camping higher and starting at the same time. Aim for first light at the Upper Saddle. It shouldn't take you more than 4 hours from there to the summit. That's about 9:30 am. Rap the Sargent's, which is already set up minus the rope, then the big rap back to the upper saddle (single rope if you use the slings and throw the rope skier's left), again, already rigged. Say two hours of being very careful, then another two back to the Lower Saddle. That's 1:30 pm back at camp for packing up and hiking down. Depending on your level of fatigue, you could do that in 4 to 6 hours for average peeps. That's the long end. Those Exum clients aren't carrying much for any of the trip and hiking times vary widely for them. Routefinding from the Meadows to the Lower Saddle in the dark, while certainly doable, can lead to some ugly talus traverses and unneeded climbing, especially between the caves and the moraine. If you need to be down early, and want to camp at the Meadows, just start at 3! The biggest challenge to moving quickly on the Owen-Spalding route is other parties. Check out the Wittich Crack variation. 5.6, starts just before the O-S so if there is a line you can pass them all.