Regular flow at day's end (8)
I believe the answer is:
eventide
'day's end' is the definition.
'eventide' can be an answer for 'end' (I have seen 'end of day' mean 'eventide' so perhaps 'end' could also mean 'eventide'). I'm unsure of the 'day's' bit.
'regular flow' is the wordplay.
'regular' becomes 'even' (synonyms).
'flow' becomes 'tide' (tiding is a kind of flowing).
'even'+'tide'='EVENTIDE'
'at' is the link.
Can you help me to learn more?
(Other definitions for eventide that I've seen before include "End of the day (poetic)" , "some time later?" , "The day's close (poetic)" , "latter part of the day" , "onset of dusk" .)