You can buy the tickets once in Cuzco, not before. This is a hardcore-backpacking experience, so you have to be flexible and be ready for a not very pleasant journey. This kind of public transportation is not exactly comfortable.
I'll advice also to avoid over night buses, but I think most of them depart in the evening as a way to make more comfortable the long journey. The reason of my suggestion is due to safety and security concerns. The road condition is not exactly ideal and it can be risky, specially at night time with a tired driver behind the wheel and limited visibility.
I wish you a safe journey,
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Thank you! We won't change our mind but your valuable opinion provides us the color how the locals see this way of travelling.
Information on destinations in Peru like Machu Picchu, Cusco, lake Titicaca, Arequipa, Paracas, etc.; and activities like the Inca Trail, the Salkantay trek, the Colca Canyon trek, etc.
I'm a tour guide in Peru and I know very well the main tourist destinations like Machu Picchu, the Inca trail, Cusco, lake Titicaca, the Nazca lines, etc.
I love outdoors and I have hiked many times the Inca trail and the Colca canyon (the 2nd deepest canyon in the world).
I also know the best places to go like restaurants, coffee shops, bars, pubs, and nightclubs in many cities of Peru.
Education/Credentials Master in Business Administration with 12 year of experience in the travel industry.