使用cron作业和发送电子邮件时CPU使用率很高

I have a website which sends daily writing reminders to its users based on their timezone and hour settings. eg: a user in New York (America/New_York) prefers to receive his reminder at 9PM. in my current implementation (after many changes), I store timezone and notify_hour in settings table and find users with a complex and heavy MySQL query. I have a website which sends daily writing remi