Perhaps watch author entering exhausted after striking editor (5)
I believe the answer is:
timer
'perhaps watch' is the definition.
(a watch times things)
'author entering exhausted after striking editor' is the wordplay.
'author' becomes 'me' (the author of the crossword).
'entering' means one lot of letters goes inside another.
'exhausted after striking editor' becomes 'tir' (I can't justify this - if you can you should believe this answer much more).
'me' inserted into 'tir' is 'TIMER'.
Can you help me to learn more?
(Other definitions for timer that I've seen before include "one of 14 [CUCKOO CLOCKS]" , "Preset mechanisation to activate a device" , "Maybe watch" , "Clocklike device" , "chronometer" .)