Different output pico/esp8266

The Pico is correct :)

On the Pico, the code executes quick enough that console.log('newtime ', newtime); is executed before the timeout created with setTimeout executes, so newtime doesn't get assigned before it is used.

If you want this to actually work, do:

oldtime = getTime();
setTimeout(function() {
  newtime = getTime();
  console.log('oldtime ', oldtime);
  console.log('newtime ', newtime);
  console.log('diftime ', newtime-oldtime);
},160);