I'd say it would depend on if you've ever heard of something like this being successful at your workplace. Different work environments have different cultures, and you can't really say "you should do X" or "you shouldn't" without being on the inside.
I'd say that, if you know of someone in your workplace who got a raise outside of the normal performance review times, give it a shot, because it's something that CAN happen, given exceptional performance. And if you haven't heard of that happening, then I'd say play it safe for the three months, while obviously pushing it hard during the designated time.
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