The American Federation of Musicians (AFM) released a feature on John Williams, and in it is a few quotes regarding The Force Awakens.
It says that recording sessions for the upcoming film began in June, and will go through this month and possibly into September. Once the film is edited and effects are added, Williams will then go back and make changes or rerecord anything that is needed before everything is completely finished. Regarding J.J. Abrams, Mr. Williams says that he has been a joy to work with, adding, "[J.J. is] a very genial, warm person. We had a few preliminary meetings and I played themes on the piano to which he responded very positively. By and large he has allowed me to do my thing, and our minds have been together on our approach to the scoring."
You can read the rest of the article over at the AFM website.