Yes, but I want to send emails to those customers who have booked passes and wanted them to aware about new timings of the event.
How often do you need to do this?
Only once and if require,will do in future for other timings.
So, you could export the members, import them into a (for example) Mailchimp list and send the mail on schedule. You'd get delivery and open reports, managed responses, etc.
Seems like setting up code to do it is work you don't need to do (and won't give you a technically better solution)
Otherwise, as Michal says, the queuedjobs module is the safest way to do it.
I think the way of Mail Chimp should work for me and will send emails without fail. But can that schedule the email time?
Like I want to send it at 6 PM today.