Problem with the delay of ChartSetSymbolPeriod()

Hi coders,

the H1 chart is open. Now I would like to have screenshots from H1, M15 and H4. I do it this way:

ChartScreenShot(0, _Symbol+(string)_Period+".png", 1280, 720);
ChartSetSymbolPeriod(0, NULL, PERIOD_H4);
ChartScreenShot(0, _Symbol+(string)_Period+".png", 1280, 720);
ChartSetSymbolPeriod(0, NULL, PERIOD_M15);
ChartScreenShot(0, _Symbol+(string)_Period+".png", 1280, 720);

As you surely know, that doesn't work because ChartSetSymbolPeriod() works asynchronous and doesn't wait for the timeframe to be changed before continuing with the code. So the result is only one screenshot of the current timeframe.

Can someone help me to solve this problem in any other way?

Thanks in advance!