Completed synthetic tests are evaluated every 60 seconds. Multi-step monitors, however, will only be evaluated once the all steps have completed, or failed. This can sometimes take several minutes, and it's why we recommend reducing the number of steps for monitors where possible.
The evaluation window configured in the alert will also significantly influence when an alert is triggered.
For example, if the last five pages of a multi step monitor with 10 steps time out, there can be a five to six minute delay in when the alert is triggered.