You do not need to loop over the list to do this. If you have the list of objects for that day which have an attribute that hold their percentage part you can use the SUM (aggregate list) activity to sum up the total percentage for that day.
Then you can check if that sum <= 100 to check that it doesn’t exceed 100%.
As bob said you can achieve this with the help of Aggregate List & an exclusive split which check your condition (Sum<=100)
To more know about , check here
I hope this helps you