NavList:

Jim,
One LD have to be very close to 18^h UT, probably less than one minute of time before 18^h. Assuming the longitude is somewhere in the interval 55°W to 60°W, the sun's altitude at that time would be above 40°, several degrees larger than the value shown in Stellarium. Thus it cannot be that time.

The other UT corresponding to the cleared LD is sometime between 18^h and 19^h UT. As it is close to a minimum linear interpolation between the given LDs wouldn't work. I have used linear interpolation of the moon's and the sun's GHAs and declinations and then calculated the LD. My result is 18^h35^m4^s UT. At this time the sun's altitude fits better. Calculating local apparent time from the sun's altitude I get a longitude around 57.7°W.
Lars