Day Blair perhaps follows old, boring routine (8)
I believe the answer is:
monotony
'boring routine' is the definition.
(I've seen this before)
'day blair perhaps follows old' is the wordplay.
'day' becomes 'mon' (abbreviation for Monday).
'blair perhaps' becomes 'tony' (I can't justify this - if you can you should give a lot more credence to this answer).
'follows' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'tony' put after 'o' is 'otony'.
'mon'+'otony'='MONOTONY'
Can you help me to learn more?
(Other definitions for monotony that I've seen before include "fixed routine" , "Unvarying tedium" , "Sameness" , "Lack of excitement" , "It's wearisome" .)