Busy period (4,4)
I believe the answer is:
rush hour
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">busy period</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for rush hour that I've seen before include "Time of day when traffic is busiest" , "Busy period to travel" , "It happens at the beginning and end of the working day" , "Weekday crush of people and cars" , "Time when traffic is at its peak" .)