Finish time. In bed at last (3)
I believe the answer is:
end
'last' is the definition.
(I know that last can be written as end)
'finish time in bed' is the wordplay.
'finish' suggests the final letters.
The last letters of 'time in bed' are 'END'.
'at' acts as a link.
(Other definitions for end that I've seen before include "Game at bowls" , "Novel by Graham Greene" , "dying > department" , "Final part" , "Closure" .)