There is a difference between the 2 things :
a noun can be an object or a subject or any other thing
so there is a difference between the nature of the word and it's function
darf makan or zaman are single words that can be used for a lot of reasons if one of the reasons is to tell us where and one the action happened in a sentence starting by a verb (jomla fi3lia )
then it's a maf3ol fih