In Mastering Bitcoin in the section on Difficulty Bits Andreas notes:
This means that a valid block for height 277,316 is one that has a block header hash that is less than the target. In binary that number would have more than the first 60 bits set to zero. With this level of difficulty, a single miner processing 1 trillion hashes per second (1 tera-hash per second or 1 TH/sec) would only find a solution once every 8,496 blocks or once every 59 days, on average.
How was 59 days calculated?
2^60 (1.15 x 10^18) would be the number of possible values to cycle through and 1 TH/s = 1 x 10^12 attempts every second but what am I missing?