This read only variable will return the hour that corresponds to the current moment based on the default time zone for the system (ie: local time). You can change the base time zone to use with the functiondate_set_timezone().
draw_text(32, 32, "The time is " + string(current_hour) + ":" + string(current_minute) + "." + string(current_second));
The above code would draw the current international time on the screen.