It takes place sometime in 2015.
In the second episode, Jessica does a search for admission records for the night she escaped Kilgrave, on January 20, 2014, and mentions that the bus crash was "a year ago".
Other anecdotal evidence
- In ep2, we see snow on the ground, but people in NYC are generally wearing light coats, or none at all
- In ep2, we see a poster on the train for something on October 6th or 8th. (this could be an old/very early poster, but it's worth mentioning)
- In ep3, Luke mentions "you, me, the big green dude and his crew"
- In ep3, a radio caller mentions "ever since those guys quote 'saved the city,' people have been making up stories about more super folk out there."
- In ep3, Trish references the Battle of New York and the alien invasion as something that was unlikely to happen, but does not mention Sokovia.
- We know that Jessica Jones happens sometime after season one of Daredevil, as the warehouse where Matt fights Nobu in Daredevil is the same one later turned into a drug warehouse in Jessica Jones. The warehouse is shown to have suffered damage from the fire in Daredevil.
- When Jessica meets Claire Temple, Claire mentions knowing and having experience with helping Matt.
Since the issue with Inhumans is not exactly a quiet one, and since there is no mention of Sokovia or the events of Age of Ultron or Ant-Man, I'd estimate that the show takes place at the very tail end of the 2014-2015 Winter season - prior to Age of Ultron and the Terrigen release.