For Peru Rail and Inca Rail, trains depart from Poroy station (a 20-minute trip from Cusco) or from Ollantaytambo station, located in the Sacred Valley. The trains arrive at Machu Picchu Pueblo (also known as Aguas Calientes). Alternatively, there are tourist busses to Hidro Eletrica from where it is a two hours hike along the railway tracks to Aguas Calientes.
To get from Cusco to the Rainbow Mountain trail head, it takes about 3.5 hours, each way. So 7 hours is spent on a return trip, travelling from Cusco to the trail head. The actual hiking is for 3 hours.
The Salkantay trek is a high altitude hike that comes with obvious altitude sickness risks. The highest altitude that you will reach on this trek is just over 4,600m (4,900m if you do the Salkantay / Inca Trail Combo), which might be the highest altitude you have ever gone to outside of an aeroplane.
You must hire a guide – This is a new rule that whilst theoretically brought in more than a year ago, has only recently been more stringently enforced.
You have to follow a set route – Gone are the days when you could clamber about on the ruins – now you need to follow a designated route as part of your tour.
You will have a designated time for entry – This is the aspect of the entry ticket that has changed the most since 2015.