If an incident is under sync, each time that there is an update - Exalate for ServiceNow will poll for that incident and run the outgoing sync processor.
If the result replica object is identical to the previous replica object or if the replica object is empty, no sync transaction will be triggered (and the change ignored)
Your requirement is met if the field 'Elapsed business duration' is not copied into the replica (and no other field changed)
Thanks - great answer. So in the below script, assuming that the only field changing is the business_duration, a sync will only happen if active = false?
if(entity.tableName == "task_sla") {
replica.incident_number = entity.task.display_value
replica.sla = entity.sla.display_value
replica.breach_time = entity.planned_end_time
replica.has_breached = entity.has_breached
replica.end_time = entity.end_time
replica.stage = entity.stage
if (entity.active == false)
replica.business_duration = entity.business_duration
}
Looks indeed correct - the proof of the pudding is in the eating 
We are setting up a syncronization of incidents and attached SLA records from servicenow to JIRA.
As i understand any change to the records will trigger a sync.
On the SLA records however, there is a field "Elapsed business duration" which is updated very frequently. We don't want to sync that field and we don't want a sync to be triggered everytime this field is updated.
Is there a way to ignore changes to this field?