It opened after 10 when we went, and Pluto's dog house and Daisy's diner opened at 11am.
It's usually open about an hour or two after regular park opening hours and closes as early as 8:30pm on nights when there are Fireworks displays. But the best way for you to check on the hours for Mickey's Toontown on the day you plan to visit, would be by downloading the Disneyland Mobile App
Thanks! Your answer is awaiting moderation.