The length of time it actually takes to WHELP is dependant on breed and litter size. Call. Your. Vet. Take the dog in. Research WHELPING! Sit down in front of your little computer for the next 8 hours and MEMORIZE everything you need to know about whelping a litter so that you know what to do in an emergency.
The integration doesn't need to be between the IVR and Envox. UUI is part of ASAI which is the adjunct interface for the CM, so it's maintained as part of the call record. Assuming your IVR adds data to the UUI field Envox CT should be able to see/access it. I'm fairly certain that Envox CT Connect exposes an interface to UUI.
Maximum size of UUI data. The size of the UUI depends on the private data version of the ASAI protocol on your specific PBX. In general UUI will be either 32 bytes (for older PBX's) or 96 bytes for newer PBX's. If you're on a CM then your UUI will be 96 bytes. Something to consider is what other applications/adjuncts are functioning in your environment and whether any of those are making use of UUI as well.