Arya says that she was blind for a full year, and she was blinded at about the same time Sam left Bravos for Oldtown. Thats the only time frame I can really find, though you have given me a very interesting thought, how long in between the time Sam is sent to Oldtown via Bravos, and the time Stannis sends Justin Massey there, surely it has not been a year. Add to that the fact that the year Arya was blind was not started until Sam and Dareon had been in Bravos for a little while, so that the trip and their time in Bravos was not included and even more time for Stannis' plot line to continue on. Now you have me wanting to re-read the Arya chapters and I don't have my books, damn.
Or was she blind for half a year, one of the two, damn I really gotta get my books.
The last clear thing I remember to synchronize timelines is that right before Arya gets her sight back, she reports that one of the things that she learned was that a slaver ship was seized by the Sealord carrying wildling refugees captured from Hardhome.