The time by which a ticket needs to be resolved/responded to without violating the SLA policy is called the due by time. It is calculated based on the SLA policy active on a particular ticket. Sometimes, admins can set up rules to send an escalation email to the supervisor or the manager when some tickets (like those raised by VIP customers) aren’t resolved/responded to in time.
In most helpdesks, the due by time of every ticket is displayed right next to it. And sometimes, they are allowed to change the due by time, preferably with the permission of the customer.
Tickets violating the response due time are usually marked as 'Response due' and tickets violating the resolution due by time are usually marked as 'Overdue'. So, agents can easily filter out tickets that they need to get cracking on using the 'Due by' filter.