A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Jorge Santos
Date: 2015 Nov 6, 13:44 -0800
After rerunning your data in StarPilot with the -7 hours offset I got:
8 am: Hc= 12 degrees 59.6 minutes
3 pm: Hc= 60 degrees 28.4 minutes
These values were displayed in StarPilot with a minus (-) signal, this is odd but anyway the absolute Hc values seems quite acceptable for your latitude of 40 degrees North. Conversely, the Hc value you got for 15.00.00 (18 degrees 7.2 minutes) would be feasible only for a higher latitude.
Hope this helps.