VADP: Time to snap a senstive application

I have a customer with an application that is extremely sensitive to any "outage", and they are very concerned about the duration a system might become unresponsive during an Avamar VADP/SNAP operation.  The vendor is telling them that the max time to be unresponsive before a failover is triggered is 500ms.   Are there any docs or guidance that we could provide the customer around this application other than perhaps an in-guest backup?

jim