With regards to change the interval automatically, if you meant changing the interval at run time after it has been set, not sure if that's possible as from http://www.tersus.com/?Id=593, it seems that the timer is a one-time timer.
Also think having changing run time interval is quite messy. Was thinking maybe a better way would be to periodically check for a certain condition or certain value in database. Based on the different values or conditions then perform action.
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