Not to be glib, but whenever you need it most is the day to stop. Its lovely to plan a day to spend in one city, sightseeing or relaxing but until you are on the Camino you don't really know how your body will react, when blisters might appear, or a strained muscle to slow you down - your body will let YOU know when its time to rest. If you have a tight schedule and only have one day to spare as a 'rest' day, why not just use it whenever you feel you need it. I've walked thru lovely big cities and thought how I'd love to spend a whole day there looking around but I've also spent a night in a Casa Rural with absolutely nothing near it for miles and thought how happy I'd be to spend the day there just relaxing and looking at the wonderful views. My advice is just to play it by ear....
I know that I am just a little bit anal, but will be trying to book auberge/hotel accommodation for my rest day - is there a stretch that a rest following is good, or a spot that is particularly memorable that someone recommends. Thanks
2002 CF: 2004 from Paris: 2006 VF: 2007 CF: 2009 Aragones, Ingles, Finisterre: 2011 X 2 on CF: 2013 'Caracoles': 2014 CF and Ingles 'Caracoles":2015 Logrono-Burgos (Hospitalero San Anton): 2016 La Douay to Aosta/San Gimignano to Rome:
Sarria is just over the half way for you from Astorga to Santiago. It is not the most scenic place to spend a rest day but it has some nice hotels and a number of shops and restaurants. From there you have your last few days walk to Santiago.
Well, Auburnfive, I think you are right in that you are trying to plan a bit too much. What has been said about taking a stop when you feel you need to or want to, is the best advice. However, there is much to be said for Sarria in terms of it being a good midway point for a stop-- there are a few interesting churches, comfortable albergues and hotels, and good restaurants, and you can take a seat in one of the cafés along the river and watch the pilgrims stroll by.
Alipilgrim's advice is good and you should really reflect further on this. Two other interesting stops, if you like the idea of a smaller place, could be Molinaseca, which is one of the prettiest villages in that part of Spain-- also with decent accommodation and food, and there are a few good spots for watching pilgrims walk by. If the weather is decent, there is a splendid riparian pool running through the middle of the pueblo.
For a very small spot, with nothing much more than the two casas rurales, look at Herrerias de Valcarce, very bucolic, where the air is clear and fresh, and you will be able to doze calmly and prepare for the next stretch. One of the casas rurales is well-placed to watch pilgrims struggle through, and the other has a terrasse angled so that you can ignore them and sip on your drink.