This is what the verse says: "For everything there is a season, and a time for every purpose" (Ecclesiastes 3:1). There was a set time for Abraham, when circumcision was given to him, as it is said, "On that very day Abraham was circumcised" (Genesis 17:26). And there was a set time for his children to be circumcised, as it is said, "for they were circumcised" (Joshua 5:5).
The Appointed Time When Abraham and His Sons Were Circumcised
Yalkut Shimoni on Nach 15:6
זהו שאמר הכתוב לכל זמן ועת לכל חפץ, זמן היה לו לאברהם שנתנה לו המילה שנאמר בעצם היום הזה נמול אברהם. זמן היה לבניו שימולו שנאמר כי מולים היו: