We recently have a situation where a group of trekkers who were trekking to annapurna base camp finished the trekking sooner than planned. The reason was that the trekkers were very experienced and they could walk for as many as 7 hours per day. While its good for them in this case as they wanted to actually see Kathmandu more, it might not be the same case for everyone.
Most trekking companies,including us make the itinerary based on the assumption that trekkers can walk for 4 actual walking hours. Add few more hours for the rest and meals in-between, the journey becomes 6-7 hours per day.But if you’ve been doing trekking since long and do not mind walking for more hours, the itinerary can be shortened as you wish. So it is always good to discuss this thing before confirming the trek.
Needless to say that, if you take care of this you can not only save a little on the cost but can manage some days to do other things after the trek. Since the hotels and guides and transportation fees and usually paid in advance and not all of them offer refunds, it might not be possible for the agencies to get refund if you finish the trekking in time which also means you do not get refund.
While the normal Annapurna Base Camp Trekking is normally 12-13 days, some people complete it in as little as 6 days. Last thing the trekking agency wants is the trekkers to get hurt because of too much work, so they make their packages keeping the average person in mind.