I have no idea about real sonars, but the limits are that they will probably expect to ping up to a kilometer.
that means 2000 meters of travel, which means you hear the echo in 2000/1500 seconds, as sound moves
roughly 1500 meters a second in seawater.
so the minimum time between pings would be just over a second.
however, pings will take a time to transmit and range might be larger.
Which means longer periods inbetween pings.
so, one second seems to be the minimum time between pings.
I expect *real* submariners do not use active pings. it's unhealthy