The math of waiting to be sitted
Without Little's law:
Assuming people leave when done at random, with one table in the establishment the departure rate would be one departure per $t$ minutes. With $n$ tables, customers would leave at a rate of $n$ per $t$ minutes, so on average you'd wait $t/n$ minutes for the next free table.
With Little's law (essentially the same argument).
occupancy = throughput rate * service time
Since the occupancy is $n$ and the service time is $t$ the throughput is $n/t$ customers per minute. So you wait on average $t/n$ minutes for the next customer to depart.