This Article is about interpret the note in the T+ Pro manual. 

The T+ Pro note in the manual states the following:

The circuit protection of the product will heat up as voltage is applied.
I would interpret this as the user can apply voltages for 30 seconds total, before needing to wait 300s to cool down.

If the technician can take the three phase-to-phase readings with a total elapsed time of less than 30s that would be acceptable.