Butterfly viewing from Zihua

In my opinion, you will need another day. The bus to Morelia is clean and comfortable, but it takes 7 to 8 hours. Day 1 would be devoted to bus travel, day two will also involve travel getting to the reserve, and day three would also be devoted to travel. Worse yet, it leaves no time to explore Morelia's historic central district which is worth a trip alone. Hope this info helps you decide.