No, it's not a race to a finish line, it's a race to find a random number that when placed in the block header hashes to a value that is less than the difficult

No, it's not a race to a finish line, it's a race to find a random number that when placed in the block header hashes to a value that is less than the difficulty. The difficulty is adjusted as desdiv said above based on the network performance in the previous period. When network hashrate increases significantly, the next difficulty adjustment happens sooner and if the hashrate dropped dramatically then it would happen slower. The better analogy would be a race to turn over stones looking for the one with the secret on the back but the number of stones was adjusted for the previous number of searchers and now with fewer searchers it will take longer for any of them to find it.