Why a picture indicator?
A graph has cursors and you can analyze the data array to locate a y value that exceeds the limit. You would get back the index in the array. You can use the index to set the cursor and as long as you know the dt of the captured data you would multiply the dt times the index to get time.
This all assumes that you are actually using a graph and not a chart and that you are using a hardware timed acquisition from a DAQ card and not single point, software timed acquisition. You would need to provide some actual details for a more comprehensive answer. Post your code.
