The hike is not as bad as some may fear. However, by all means take 24 or more hours to acclimatize yourself to the altitude so you do not succumb to pulmonary edema. I volunteered for the Ski Patrol at Alta, Ewtaw for years and it was just expected that every day some fools from sea-level in California would fly into SLC at 7:00 AM, rent a car and check into their rooms by 8:00 AM, slap on their skis and then around 10:30 and for a few hours afterwards become faint, develop nausea, chest pains, and quit breathing -- making a change in altitude from almost sea level to 8,000 feet within 4 or 5 hours is a great way to kill yourself. Stay in Cuzco for at least one day (better, stay there for two and begin the hike about 5:00 AM) then when you get to the ruins you'll have made it there before the first tourist train and have the unique experience of being a Machu Pichu almost completely alone. It's one of the most beautiful places on earth until the train tourists show up complaining about it being too cold, too humid, too hot, too not like their living rooms.
Good luck.