I judge the rate of decel based on the big picture, not many traffics around, late night arrival, just let the aircraft decel by itself, busy hours and following someone on the arrival, reduce asap. Sometimes, ATC will issue a more specific instruction, i.e. "Reduce
now to 250kt", then comply accordingly.
At the end, just use your airmanship and good judgment and get the job done.
No cookies for using spoilers all the time
