Can the daily hiking distance or duration be adjusted?

I'm happy with the overall distances but my knees are rather worn – can we adjust the itineraries to reduce the amount of time climbing and descending at the start and end of the trek?

The campsites for the treks are fixed by Bhutan's tourism authority and the Department of Forestry, so adjusting trekking itineraries is not always easy. On certain days it might be possible to add an extra day or a rest day, but otherwise you'll usually need to spend the night at the designated campsite. I would advise against trekking if you have knee issues – a good alternative is to take a standard tour with lots of day hikes throughout.