Yes, you can wait till summer's end to remove the stains. However, you might want to go ahead and get everything you need to remove the stains, now, for two reasons.

First, it may be difficult to purchase what you need, in September. --I don't know that it will be, but I do know that many retailers are trying to clear out pool stock.--

Second, if you get it now, you can use small (1/3 - 1/2 recommended ) doses plus a CuLator (under a skimmer sock) to avoid having stains get worse.

From what I can tell from Periodic Products literature the CuLator bags do NOT have a life expectancy -- they are still good, till they've absorbed all the metal they can hold OR are gummed up with pool goo (thus, the skimmer sock).

Regarding the