In a second version I'm thinking of using a larger touch LCD display and adding a DS3231 (RTC) disciplined to the GPS 1hz to handle timing.  I've been playing with this using an esp32 and tracking the offset time between the GPS and RTCs 1h pulses as input to a PID algorithm and driving the DS3231s aging offset register to sync them. 

The biggest issue I have run in to is the GPIO interrupt latency is typically just under 2us with occasional jumps to 10us! I'm currently averaging the last 10 deltas and using that as input for PID as a work around.  With this I seem to be able to keep the RTC to within +/- 2us of the GPS 1hz signal.