Using OnTimer() inside a custom indicator created with iCustom() is not working.

[metaRaider]

I have created a custom indicator using...

int indicatorHandle = iCustom(symbol, PERIOD_M1, "MyIndicator");

..and at some later stage, I attach it to a new chart that I have created...

long chartHandle = ChartOpen(symbol, PERIOD_M1);
ChartIndicatorAdd(chartHandle, 0, indicatorHandle);

I believe the custom indicator is correctly attached to the chart because the OnChartEvent() function is correctly processing messages.

Inside the OnInit() function of the indicator, I create a 1 second timer using EventSetTimer(1), but the timer is not firing at all (OnTimer() not called).

I then wondered if it was not firing because the timer in the indicator was created and running for some time before being attached to a chart, so I modified the EA to post a message to the indicator once the indicator was attached to the chart. I then create the timer at this point...

void OnChartEvent(const int id, const long& lparam, const double& dparam, const string& sparam)
{
   if (id >= CHARTEVENT_CUSTOM)
   {
      ushort eventType = (ushort)(id - CHARTEVENT_CUSTOM);
      
      if (eventType == CHART_EVENT_CREATE)
      {
         // TECH: This event is received when...
         //       1) The EA creates a new chart.
         //       ...and...
         //       2) The EA attaches this event handler to the new chart.
         EventSetTimer(1);
      }
   }
}

...but still I am unable to get the timer to fire. I have checked GetLastError(), and there are no errors.

So my question is, should this work or will the OnTimer() only work in an EA?

If this should work, and I hope that it should, can someone please highlight where I am going wrong.