First of all, routinely attend thus in office — nine to five, say (5)
I believe the answer is:
ratio
'nine to five say' is the definition.
I can't tell whether this definition defines the answer.
'first of all routinely attend thus in office' is the wordplay.
'first of all' indicates taking the first letters.
The initial letters of 'routinely attend thus in office' is 'RATIO'.
Can you help me to learn more?
(Other definitions for ratio that I've seen before include "Correlation" , "Relationship between two numerical quantities" , "Proportion of one thing to another" , "nine-to-five, say" , "eg 1:3" .)