OK
No progress in nailing that "state" deal.
I went back to the shop, as it were, for what I could hammer out on my own.
Using...
const byte led_pin = 13; // using on-board "LED D13"
const long time_on = 100;
const long time_off = 900;
unsigned long change_pt = 0;
void setup()
{
pinMode(led_pin, OUTPUT);
}
void loop()
{
change_pt = (millis() + time_on);
while (millis() < change_pt)
{
digitalWrite(led_pin, HIGH);
}
change_pt = (millis() + time_off);
while (millis() < change_pt)
{
digitalWrite(led_pin, LOW);
}
}
...the blink stays in sync with the klacker on WWV.
It's likely not roll-over proof and if I've minimised the effect of any cumulative error, unlikely, that was purely by accident.