The term I learned is SWAG -- Scientific Wild-A*** Guess.
Without reading through all of your text, I'd say you're having a problem subtracting 7-digit numbers with 6-digit floating-point precision. There's a reason the Unix time() function returns an integer time in seconds rather than floating point.
What are the engineering and design challenges in creating successful IoT devices? These devices are usually small, resource-constrained electronics designed to sense, collect, send, and/or interpret data. Some of the devices need to be smart enough to act upon data in real time, 24/7. Are the design challenges the same as with embedded systems, but with a little developer- and IT-skills added in? What do engineers need to know? Rick Merritt talks with two experts about the tools and best options for designing IoT devices in 2016. Specifically the guests will discuss sensors, security, and lessons from IoT deployments.