When we talk mathematically about speed, it is calculated as the distance traveled divided by the time it takes to travel that distance (it only has magnitude). It can be defined also in terms of other quantities besides distance, depending on the context. In physics, speed is often defined as the rate of change of position over time, which is commonly expressed as distance traveled divided by the time taken to travel that distance, as mentioned earlier. In certain situations it can also be defined in terms of other quantities such as: angles, phases or displacements.

Your question can therefore not be answered because it is incomplete. Neither the first nor the second.

You could count the steps performed or keys tried and divide the total by the total time required. Then you would have keys/sec or steps/sec as the result, depends on your needs.
But you can't calculate 52bits/30sec and claim that you can work out 0.577 sec per number of bits, and of course you know yourself why that is. Because otherwise you would have already solved the entire puzzle hundreds of times