Lesson 1 of 3
What a Timer Event is
A Timer Event is triggered by time. It answers the question: what happens if we wait too long? — or more precisely, what does the process do when a specific time condition is met?
Timer Events are represented by a clock icon inside the event circle. They appear as Start, Intermediate, and Boundary events, each with a different role:
| Timer type | Placement | What it models | Business example |
|---|---|---|---|
| Timer Start Event | Start of a Pool | Process triggered by a scheduled time | End-of-month payroll batch; daily report at 9am |
| Timer Intermediate Event | Within the flow | Process pauses for a defined period before continuing | Wait 3 business days for customer response before sending a follow-up |
| Timer Boundary Event (interrupting) | On the edge of a Task | Cancels the task if not completed in time; triggers escalation | SLA breach: 'Approve Invoice' not completed in 48h → escalate to Finance Manager |
| Timer Boundary Event (non-interrupting) | On the edge of a Task (dashed border) | Starts a parallel action without cancelling the task | After 24h on 'Approve Invoice,' send a reminder — task remains open |
Why BAs should care about Timer Events
SLAs become process rules
A diagram that says 'Approve Invoice' without a timer is making an implicit assumption that approval will happen in a reasonable time. Adding a Timer Boundary Event converts an implicit assumption into an explicit process rule — and that rule is a business requirement. Without Timer Events, BPMN models do not capture the SLA commitments that are often the most critical requirements in a process improvement project.
Interrupting vs. non-interrupting
The border of a Boundary Event tells you whether it is interrupting (solid border) or non-interrupting (dashed border):
- Interrupting (solid border): When the timer fires, the task is cancelled. The flow leaves the task and follows the exception path. The original work stops. Use for: SLA escalations, process timeouts, deadline-based cancellations.
- Non-interrupting (dashed border): When the timer fires, a parallel action starts — but the original task continues. Use for: reminders, notifications, monitoring actions that run alongside ongoing work.
Concrete contrast:
A support ticket SLA breach uses an interrupting Timer Boundary Event — when the 4-hour timer fires, the agent's task is cancelled and the ticket is escalated to a senior engineer. The original agent cannot continue working on it.
A reminder to an approver uses a non-interrupting Timer Boundary Event — after 24 hours, a reminder email is sent, but the approval task remains open for the approver to complete.
✓ When to use
- Timer Boundary Event (interrupting) when a task has an SLA and a breach changes the process flow
- Timer Boundary Event (non-interrupting) for reminders and notifications alongside active tasks
- Timer Intermediate Event when the process genuinely waits for a fixed period before proceeding
- Timer Start Event for scheduled or batch processes
✗ When not to use
- ✕Don't add a Timer to every task just to document that it has an SLA — only when the breach changes what happens next
- ✕Don't use a Timer Intermediate Event as a substitute for a process-level wait when the wait has no impact on the flow