can be added as soon as the tank is at the correct temperature and the salt mix has circulated for 24 hours. The cycle starts when you add a source of ammonia, not a source of bacteria. The bacteria need ammonia to live, that what they eat. Uncured LR
is INO the best way to cycle a tank.
David, I hate to damper your enthusiasm for this hobby but a tank that small is very hard to maintain. Things can go wrong very quickly and there is not enough water volume or beneficail bacteria to you time to react to a situation.
Please read throuhg the articles section on this site and GO SLOW. Take your time to understand all aspects of your tank and you may end up with a beautiful nano tank.
BTW, that tank is too small for 2 clowns. Maybe a couple of purple firefish at most.