Weekend day — is overseeing workplace? OK (12)
I believe the answer is:
satisfactory
'ok' is the definition.
(similar in meaning)
'weekend day is overseeing workplace?' is the wordplay.
'weekend day' becomes 'Sat' (abbreviation for Saturday).
'overseeing' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'workplace?' becomes 'factory' (type of workplace).
'sat'+'is'+'factory'='SATISFACTORY'
(Other definitions for satisfactory that I've seen before include "unexceptional" , "Good enough" , "fine" , "Fully acceptable" , "Fulfilling expectations" .)