Reminder emails

We have set in general settings, send reminder emails for provider and clients to yes, we have set 8,1 for providers and 4,1 for clients on when the emails should be sent out to them.

I have notice that the reminders do not get sent on schedule, it gets sent as soon as someone access the site.

For example: I had a appt schedule at 3pm today, provider was suppose to receive an reminder email at 7am (8hrs before), but they did not receive it till 10:48am (the time I access my site). The client did receive an email at 11am (as schedule, cause I was still on my site).

Do we have to have someone access our site every hour for the reminder emails to be sent out as schedule?