You are assuming quality applicants are evenly distributed in terms of time of application - they aren’t. If you cut off at 100, you will only get a sample of people spewing fully automated application bots which mostly aren’t what you want.
"Being online during the short time" heavily favors bots. In a way, AI screening tools saved us from the future of everybody buying resume-spamming-as-a-service because it became as important to use these as getting a college degree.