This might be too late as well, but I would not recommend walking from Jaca to San Juan de la Pena via Atarés. I found the going very difficult-- even the CSJ guide by the late Maurice Fox admitted this-- and it was quite tiring. Even more difficult is the hiking path from San Juan de la Pena to Santa Cruz de los Seros.
I would recommend going by the road from Santa Cilia to S J de la P-- take a taxi one way if you are pressed for time. San Juan de la Pena is a UNESCO World Heritage site and deserves to be so: it is one of the most spectacular things to see in Spain, combining cultural, religious and political history, with astonishing vistas reminiscent of one of Maxfield Parrish' works, and exquisite carvings, seven centuries old, but fresh as the day that they were made.
I was too tired to go further and stayed at the Hotel de Aragon by the junction of the N240 and the road from the Monastery, but a friend stayed at the albergue at Santa Cilia 5 km west, and spoke very highly of the facilities and the hospitalera.
San Juan de la P was the best and the worst day of my 2005 Camino, but it is too extraordinary to be missed.