Timer in developed app running slow on Forerunner 935

Are you using a one shot or repeating timer? The doc implies that repeating timers can have skipped executions:

developer.garmin.com/.../Timer.html

If a repeating Timer fails to run before its next execution time, then any missed executions will be skipped.

Maybe it's also possible that either a one-shot or repeating callback could be delayed (due to other stuff going on in the system, or even due to the amount of time your callback takes to execute.)

Either way I probably wouldn't try to rely a timer callback being fired after *exactly* the specified amount of time. e.g. If you have a 50 ms timer which repeats, I wouldn't assume that when it fires 20 times, exactly 1 second has passed.

For example I have a stopwatch app that uses a 50 ms one-shot timer to update the screen, but I don't assume that 50 ms actually passed between the scheduling of the timer and the timer callback. I use System.getTimer() to determine the elapsed time between any two "events" (like starting the stopwatch and displaying the current stopwatch value). That method should be pretty foolproof.

e.g.

var startTime;
var timer = new Timer.Timer();

// call this when the user presses START or whatever
function initializeTimer() {
  startTime = System.getTimer(); //get the uptime in milliseconds
  onUpdate();
}

function scheduleUpdate() {
  timer.start(method(:onUpdate), 50, false);
}

function onUpdate() {
  var now = System.getTimer();
  System.println("The current timer time is " + (now - startTime) + " ms");
  
  // Update the screen, etc
  
  scheduleUpdate();
}