Can that 2.5nm minimum separation can be less than that with TBS?
No. TBS is only allowed to provide the equivalent time adjusted for the wind, down to 2.5nm. The minimum radar separation is still 2.5nm, BUT in the tower we can use other visual separation with caveats less than 2.5nm. This is usually when one is flying a different speed, good weather and both in communication with us. Anything less than 2nm will result in a go around as there wont be time for the first aircraft to get off the runway.