The highest mountain pass in the world, the Thorang La pass was one of the highlights of my Nepalese adventure. Generally, the passage is used from Manang to Muktinath, which is also the easiest and safest way (there are possible stop-overs which the opposite way doesn't have).
In terms of walking time, it is possible to go between these two points in a day, for a quick walker, but the wisest thing to do is make a stop in Thorong Phedi or at Thorong High Camp, the latter allowing you to take advantage of a night for acclimatisation to avoid succumbing to altitude sickness.
I strongly recommend that you only consider this pass in the months of March-April and October-November. The rest of the time, there is an increased risk of avalanches and storms. In any case, it is fully worth the effort!
*After the powerful earthquakes which struck Nepal in April and May 2015, the country is being rebuilt little by little. This article was written before the disaster.
Thorang La is THE stage that everybody talks about throughout the trek: 'Will I get there?' 'What time should I go up?' then 'It was cool' 'It took me this much time...' etc.
It must be said that it's quite crazy to reach such an altitude 'so easily'. After a night in base camp you have to go straight towards the pass with your feet sunk in the snow but on a path which is been well marked out by the thousands of other walkers who've already used it. The landscape, immaculately white, is breathtaking... And one completely surreal thing is that even all the way up there you can warm yourself up with a good cup of tea in a little cabin which acts as a cafe all season!
The 1100 metres of positive height difference strangely didn't seem so difficult to me (I had taken a good amount of time to get acclimatised), it was rather the descent towards Muktinath (at 3800 metres) that made my legs sore... But still in such an amazing landscape you can forget about your pain! If you also ever go on this trek during your trip to Nepal, you'll understand why it has such a reputation... It's amazing from start to finish, absolutely recommended!
I must add that I visited Nepal before the 2015 earthquake so it's possible that places have changed a lot since then.