Do you know what the source of the lag is? There's a concept of "rounds" in IRV, but if you have access to computers, a "round" should resolve in less than a second, if election data is digitized. Is the lag digitizing the votes in the first place?
https://twitter.com/AntonyGreenABC/status/140752370034202214...
Absentee votes. Also, voters have some time to “cure” mistakes, e.g. forgetting to sign their ballot envelope.
TL;DR Nothing intrinsic to IRV.