To insure that email is responded to promptly, FogBugz can set a due date for every mail message that comes in. This is configured for each mailbox under Admin | Mailboxes.
When you set a due date, you can set it in absolute time, e.g. 4 hours. But realistically, unless you provide 24x7 customer service, you'll probably want to set due dates in working hours or days.
Example:
Any FogBugz administrator can set up your company working schedule using Admin | Site Working Schedule. You can set up the days of the week when you work, the hours of each day when you work, and you can provide a list of holidays when you don't work at all.
Escalation Reports
Anyone can sign up to receive escalation reports via email, by checking the appropriate box on the Options screen. An escalation report is sent early every morning, and lists all cases which are either overdue or which will become due that day.
If you are using FogBugz AutoSort to block spam, escalation reports will not include cases that have been sorted as spam, because all due dates are removed from cases in this area.
To look a bit further into the future, you can set up a filter to list bugs that are going to be due sometime in the future and sort that filter by due date. For example, you might set up a filter listing all cases due in the next 2 weeks, in order by due date, and check that filter regularly.