How long should it take to replace nework servers and transfer all user dat

We are planning to replace our old servers with a blade center and with Virtual servers using VM ware. We have about 220 users. Essentially the hardware is in place and the virtual machines configured.

I would like an idea of how long would be reasonable to test, do minor configurations and do the transfers, Data and Mail.

I want to know because I think I am being played, The network boys have been playing with this for 4 months and they want another month….I am looking for a reality check.