What Exactly is a Snapshot, and Why Does it Matter?

With forks, there is a snapshot date, where a snapshot of the ledger is captured. The snapshot happens at a block number, the block number is important with forks, the calendar date is only important in understanding when the block number occurred. Thus, in general, if one wants to “be in for the fork,” and thus get “free coins” they must have their transaction added to the ledger before the snapshot occurs.



Credit: https://cryptocurrencyfacts.com/understanding-hard-forks-cryptocurrency/