There is no published criteria, but any movement of a major structural member like a nose gear leg is not good.
If the movement is very slight, it is not necessarily a safety of flight issue at this point, but once movement is happening, it will only get worse and likely become more difficult to correct.
Sometimes it can be resolved with a new bolt (close tolerance may help if regular bolt is still loose). If that doesn't do it then a tapper pin is an option.
Doing a condition inspection on an RV should of course include researching compliance with Service Bulletins, but a loose nose gear leg warrants taking a specific look at
THIS ONE.