Since the variables are so dependent on your environment is to do a few test runs with smaller machines to gauge what type of data troughput you get and use that as a benchmark to calculate the P2V times -
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To my knowledge time taken for P2V will very much depends on below factors;
1.size of the disk on the server and size utilized.
2.Network bandwidth of your environment.(network utilization while doing P2V)
3.Inter site or intra site