Method to free up timer and redefine ISR used by delay()/millis()/micros()

[brycecherry75]

For my particular application, I need to free up an available timer used by delay()/millis()/micros() for another purpose while retaining the use of delayMicroseconds() which is not used by a timer along with placing my own code in the particular ISR thereof and I am looking for a method to do so.

[matthijskooijman]

@brycecherry75, if your request is about AVR boards, see arduino/ArduinoCore-avr#320 which, I think, should allow you to do what you want to do. If so, it would be good if you could test it and provide feedback in the PR, which should help with getting it merged.