Well yes but you have to remember that before bitcoin was created, there were no "target" to even begin to mine a block to see how much it would take.
So at first one would write the mining code then benchmark it to see how many hashes per second it can compute using different CPUs that existed at the time, then decide on how much time one wants between the blocks and finally using these two values (hash/sec & desired time) set the target so that it takes that much time on average.

It would make very little sense to first select a random target value then see how much time it takes with your hashrate to mine that block and then set the difficulty adjustment period. It has to be the other way around.