Day Trips vs. Extended Stays
If you're going to Tepoztlán or Valle de Bravo, you should plan to overnight. Two nights in either city would allow you to do a side trip to the ruins of Xochicalco (from Cuernavaca) or to the Parque Nacional Nevado de Toluca (from Valle). You can visit Puebla on a day trip, but it would be a shame to rush it. Moreover, the city is lovely at night, when the buildings around the zócalo are floodlit, and the sidewalk cafés fill up. If you do overnight, spend the first day seeing the city and the next day in nearby Cholula or at the ruins of Cacaxtla. You might want to leave some flexibility in your schedule for an overnight stay at the magical Hacienda Soltepec outside of Tlaxcala.