So I made zero progress trying to solve this using UNIX time. Seems like time in general is my kryptonite.
Not being one to give up, I made adjustments to the timer0 to enable the use of millis() again.
I managed to get the elapsed timer function to work using millis(), but broke my pause function. I suspect, since millis() uses an interrupt AND I’m using an interrupt to bool a flag for the pause function I’ve now got a conflict with interrupts.
I’ll post the updated code Monday. Any suggestions are welcome!