Projected Sub...

[Chess Ref]

At our HS meeting last night the question came up about projected subs.

The example used is as follows, Team batting wants to sub #25 in for #30.

#30 isn't due to bat until 5th in the inning. We had a blue make a somewhat reasonable argument that we shouldn't accept that substitution until it was #30's turn at bat. His reasoning was that at that point it's a projected sub.

I looked through the rule book and couldn't find anything to clarify.

Any thoughts?