A subterranean tool that is self contained for actuation can be run into a desired location on an automatic set mode controlled by a timer. If a problem develops in getting the tool to the desired location in time a magnetic field created by permanent or electro-magnets can be brought to bear on the tool to stop the timer before the tool actuates. Once the tool is subsequently positioned at the desired location another magnetic field can be brought to bear near the tool to set it. Alternatively, the tool can be run to the desired location without activation with the timer and then the magnetic field can be brought to the tool to set it. The magnetic field can be lowered to the tool with wireline or can be dropped or pumped past the tool to actuate the tool. Optionally the field can be generated from within an object that ultimately lands on a seat to provide a backup way to set the tool using tubing pressure.