It depends on what color of Yoshi you get to begin with. If you got a green one and reset, you would wait 9 minutes to get a blue one. If you got a red one, you'd only wait 2. Sometimes it goes screwy and resets to green when it's not supposed to, I've found. Just try again, eventually it'll go correctly.
Also, It's a bit unclear to me when to start timing. Logically, you'd start timing right after you press reset, but unless you're trying to get black or white it'd be safe to start timing at the battle's start. It's not like you only have one moment, you have a range of 2 minutes to get blue.
