Hi,
I'll be the release manager for Tails 2.12, which is a major release scheduled on 2017-04-18. The list of tickets targeting Tails 2.12 can be found here:
    https://labs.riseup.net/code/projects/tails/issues?query_id=238
Below you'll find the preliminary release schedule for Tails 2.12:
* 2017-04-06:
   - Feature Freeze: All feature branches targeting Tails 2.12 should
     be merged into the `devel` branch by noon, CET. I'm open to make
     exceptions if you can be online and responsive during that
     afternoon, but ask me first!
   - Build and upload Tails 2.12~rc1.
   - Start testing Tails 2.12~rc1 during late CET if building the image
     went smoothly.
* 2017-04-07:
   - Finish testing Tails 2.12~rc1 by the afternoon, CET.
   - Release Tails 2.12~rc1.
* 2017-04-17:
  - All branches targeting Tails 2.12 *must* be merged into the
    `testing` branch by noon, CET.
  - The upcoming Tor Browser is hopefully out so we can import it.
  - Build and upload Tails 2.12 ISO image and IUKs.
  - Hopefully start testing Tails 2.12.
* 2017-04-18:
  - Finish testing Tails 2.12 by the afternoon, CET.
  - Release Tails 2.12 during late CET.
Testers, please let me know:
* if you are available on 2017-04-06, late CET
* if you are available on 2017-04-07, morning to afternoon, CET.
* if you are available on 2017-04-17, late CET
* if you are available on 2017-04-18, morning to afternoon, CET.
Cheers!