The speed at which some work should be done (5)
I believe the answer is:
tempo
'the speed at which some work should be done' is the definition.
'tempo' can be an answer for 'the speed' (I've seen this before). I'm not certain of the remainder of the definition.
'the speed at' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'speed at' becomes 'empo' (I can't explain this - if you can you should give a lot more credence to this answer).
't'+'empo'='TEMPO'
Can you help me to learn more?
(Other definitions for tempo that I've seen before include "Pace - pacing" , "Rhythm or speed as in music" , "Rhythm, metre" , "Rate and rhythm in music" , "Muscial time" .)