To brute-force a specific 64-bit ID, sure. But if your only requirement is that the ID consist of two random characters, then a run of one character, then a run

To brute-force a specific 64-bit ID, sure. But if your only requirement is that the ID consist of two random characters, then a run of one character, then a run of another character, the time can be cut dramatically, since there are tens of thousands of 8-byte sequences that fit this pattern, and you can simply stop as soon as you find one of them.