The snapshot will be taken on block 437000 in early November (subject to change).
Pick a block number randomly out of range of blocks, e.g. 437000-438000, after the last block in the range is closed.
What for?
This way nobody will know exact number in advance. More mystery, less possibility to game the distribution.
Since there is no way to game it, certainty is way better than mystery
A possibility to game it by exchanges using user's funds was mentioned above, and this is a valid concern. Knowing the block number of snapshot in advance may help them to move funds around to get more bytes. Of course, making the number to be random still does not exclude all possibilities to game the distribution, but at least this could make it more difficult to plan ahead.
What kind of moving funds around will get them more bytes?
From exchange wallets into personal wallets and back after snapshot is taken. This can be done by exchange employees without their boss even knowing about it, if they know when snapshot is going to happen. This is just one example.
Oh no, please don't deal with exchanges where employees can take coins so easily.
I don't, and always tell everybody not to do this. But people still use them and give them a shitload of their BTC, which those scamers are going to use to game your giveaway. And when they will get 99% of your bytes, they will dump them at their exchanges and drop the price into shit. MWHAHAHAHA!!!