Shown below is data for Lyle Fork 9650' in Yosemite backcountry, somewhat like certain areas in the Whitney area but this watershed is pretty large and there are lakes upstream. There are very few High Sierra gauges out there for streamflow and this one is currently out of service.
Data plotted is from late June 2014 (a dry year).
Note stream stage fluctuated daily about 1.2' The peak occurred around noon, leveled off all afternoon then dropped fast starting around 6pm. Low flow and best time to cross was between 4am and 8am.
This example illustrates the general trend for high elevation creek/river crossings. As you move downstream to lower elevation things change and the peak can occur in the evening and best time to cross might be in the afternoon.
