Yes doing things now can have good side effects, but unless something changes in the side-effect processes, doing things later should have exactly the same sort of side effects. And because of positive interest rates, you can do more later, and thus induce more of those good side effects. (Also, almost everyone can trade time for money, and so convert money or time now into more money or time later.)
For example, if you can earn 7% interest you can convert $1 now into $2 a decade from now. Yes, that $1 now might lend respectability now, induce others to copy your act soon, and induce learning by the charity and its observers. But that $2 in a decade should be able to induce twice as much of all those benefits, just delayed by a decade.
In math terms, good side effects are multipliers, which multiply the gains from your good act. But multipliers are just not good reasons to prefer $1 over $2, if both of them will get the same multiplier. If the multiplier is M, you’d just be preferring $1M to $2M.
…I think one should in general be rather suspicious of investing or donating to groups on the basis that they, or you, or now, is special. Better to just do what would be good even if you aren’t special. Because usually, you aren’t.
There is more here.