Time period regularly featured in diary (3)
I believe the answer is:
day
'time' is the definition.
(day is a kind of time)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for day that I've seen before include "24 hours" , "Period of time" , "24-hour period" , "24 hour period" , "Twenty-four hours" .)