What is the technical name for the “time boxes” on an instrument approach plate?
Per the FAA Aeronautical Chart User’s Guide for Terminal Procedure Publications, in the revision effective 29 March 2018 on pages 30 and 31, it is a Time/Distance Table.


  Time/Distance Table
  
  When applicable, a Time/Distance Table is provided below the airport sketch. The table provides the distance and time
  that is required from the final approach fix to the missed approach point for select groundspeeds.