Jet engine throttle-down time
There’s no “throttle down” per se in jet engines.  However engine thrust does not vary linearly with spool speed and most engines operate within the 70-100% of maximum speed, with most of the thrust range between 85-100%.

In addition, there is a lag time for the engine to “spool up” from an idle power setting to effective thrust output which has to be taken into account during operation.  This is one reason that most jet aircraft have speed brakes.  They allow the pilot to maintain a higher thrust setting which allows for quicker response time to thrust lever inputs for a given airspeed at the expense of more parasite drag and fuel consumption.  Critical areas of flight such as VFR patterns, instrument approaches, short final, and go arounds, where near immediate thrust response is required makes this a useful flying technique in jets.