I'm not the expert, but it sounds like there's some confusion regarding resting heart rate and, maybe, minimum heart rate?
When using HR to track training and what-not, I think the important thing is that you establish a repeatable baseline, and use that for comparison. First thing in the morning is good because there's minimal impact from food (caffeine, sugar, etc.), stress, and you're rested, more or less. So the test conditions are pretty much the same. And most people who take their RHR first thing in the morning actually usually have to get up and take a whiz first, then lie back down for several minutes to let their pulse settle back down.