It's normal for us to turn up late to some extent (5)
I believe the answer is:
usual
'it's normal' is the definition.
(I've seen this before)
'us to turn up late to some extent' is the wordplay.
'to turn up' says the letters should be written in reverse.
'to some' says to take the initial letters.
'extent' becomes 'au' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The first letter of 'late' is 'l'.
'l'+'au'='lau'
'lau' in reverse letter order is 'ual'.
'us'+'ual'='USUAL'
'for' is the link.
Can you help me to learn more?
(Other definitions for usual that I've seen before include "Typical" , "Normally done" , "Customary, routine" , "Ordinary" , "Typically done" .)