Is the snapshot hour known?
I assume it starts from the time of a particular block on July 14th. The official Ardor thread says snapshotting will stop at
block 1,000,000 on October 12th, 2016. However it doesn't say what block snapshotting will start at, only that snapshotting starts on July 14th.
Snapshots will start be taken on an hourly basis, starting on July 14th to October 12th. Then, your total NXT will be averaged, and you'll receive that amount in Ardor tokens on October 12th, which will be freely tradeable up until the Ardor system launches.
At block 1,000,000 on October 12th, 2016, snapshotting will stop, and you'll be allowed to trade your Ardor tokens in NXT 1.9 in preparation for the launch of the Ardor blockchain.