The length of time depends on so many factors: if you already have a custom rig that you know how to edit, or how comfortable you are with scripting/rigging... with sculpting/3d-modeling... how capable your workstation is... how much time you have to dedicate to trial-and-error for all the various settings and components that comprise the Ziva sytem... what kind of characters or animals you're trying to build... the kind of shots you're trying to build for (including: can you animate well? or apply and alter motion capture data)... and the level of fidelity you want to achieve
getting to this point down below has taken me probably 2 years +, if not 3+ years, if you include all my time prior to getting serious about Ziva, learning how to sculpt and rig (and not to mention, the help and guidance and clues I've received from the Ziva team and a few others here on the forums)
and the first link shows how my rig/simulation can hold up doing even a rolling moCap animation (because doing something like maintaining the volume of the abdominal region throughout a movement like that proved to actually be very challenging, at least for me)
so it also depends on the quality you're aiming for
if you or your clients don't need or care about stuff like that, and want to do more simple poses and animations, or plan to shot sculpt more... the time it'll take will be a lot shorter.
Ziva Dynamics used to offer a pair of Human assets, ready for moCap plug-and-play, for $8,800 for studios, which they recently removed, when adding the ZIVA RT beta page on their website.
However, there are currently two Ziva tutorials I'm aware of:
The $749 one approaches it from building from scratch, and the $149 walks you through the Ziva Transfer method, which from what I've gathered, covers pretty much transferring a working Ziva Rig--such as with Ziva Dynamic's free downloadable asset of Mr. Ink--onto another compatible Rig