I want to run some code on a ATTINY85 which is also using virtualwire. I want a timer to run in the background so that after a certain period (say five minute), the sleepmode function is called. This is so that if I forget to turn it off, it effectively turns itself off to save batteries and needs to be reset (or turned off and on again) to work again.
An obvious way to do this is with millis() but as others have found, millis() doesn't work with the ATTINY85 if virtualwire is also running.
Is there a way to use the watchdog timer function to achieve what I want? Or another way?