Delay in receiving eSignLive callback for event notifications

Our main use case is for our system to wait for document signing to get completed and for this, we rely heavily on eSignLive callback notifications. Typically, we receive the callbacks with just a few seconds delay upon actual signing. Recently, we've noticed that this sporadically take longer than expected, between 12 to 22 mins. What is the normal expected turnaround time for event notifications?