Delay vs Timer vs Millis - Solved

[ScruffR]

When done right that's no issue since unsigned calculations don't care for the roll-over.
The result of (smallUnsignedNumber - bigUnsignedNumber) will not give you a negative but the expected difference as if you had an extra bit allowing the "smallUnsignedNumber" count past the roll-over limit.

That's why you often see code like this

  if (millis() - msLastPublish < period) doNothing();

See here

Millis() and rollover tutorial

The millis() function is handy for timing things with the Particle Photon (and Electron, and Core). It executes very quickly and has a good resolution (milliseconds). From the manual: Returns the number of milliseconds since the device began running the current program. This number will overflow (go back to zero), after approximately 49 days. Note: The return value for millis is an unsigned long, errors may be generated if a programmer tries to do math with other datatypes such as ints. Now…