Guesstimate on How Long to Move 350 GB Exchange 2010 DB to new Drive Array

We're running out of space on our database drive on Exchange 2010 and I need to move one of our databases to a new drive array.  The database is 350 GB and I have no idea how much downtime to expect.  Can anyone share their experience as far as downtime during a similar operation?  I'll be moving the database from a 15K 6 gbps SAS RAID 10 array to a 7.2K 6 gbps SAS RAID 10 array.

Thanks!