That depends on how you play it and how quick the character is on the uptake. There's not going to be an announcement about it, but depending on what they may accidentally wish for it may become obvious that something is up. And then they may burn through all their wishes, not realizing there's a limit. Or they may be completely ignorant about it and use all five on small things they'll barely notice. Or maybe they'll luck out and have someone tell them before they've even used one. Or they may not use any at all.

All up to you!