What does the cryptic crossword clue "Clock where time speeds up gradually, all concluding (4)" mean?

The definition is "Clock". The wordplay uses acrostic. last letters of "time speeds up gradually," = ESPY; definition: "Clock" The answer is Espy.

Clock where time speeds up gradually, all concluding (4)

Telegraph Prize Cryptic #3065 | 24 Down | 2020-07-19 flower