It is unclear when Final Destination 6 & 7 will take place, but many people speculate it will be a prequel to Final Destination 5. During a part in Final Destination 5, where Sam Lawton is talking to William Bludworth, William talks about how he has "seen this before", meaning that there had been an incident (or incidents) before Final Destination 5.
Unfortunately no official information has been given out on it yet.
In this Video Tony Todd talks about Final Destination 6 and some info about his Character in Final Destination 5.
The first picture below is a (poor quality, yes) screenshot of the official Final Destination franchise English Wikipedia page. This may be false, but it is dated as July 17 2015 (this edit was made July 19 2015) and it seems a possibility.
Final Destination 6 has been scheduled for release in 2017. Though as of July 2017 no official information has been given out.