Look at the bottom of the image. PrimeGrid WUs...Time Left column... 317 days left. Deadline 6/5/2013.
Is this a new math? Time travel? I'm confused!
Sorry if I put this in the wrong folder...
(http://i.imgur.com/m9qDKH2.png)
This is a BOINC thing, it will depend on the project or the BOINC client version.
Normally it should correct itself when tasks are reported and you get new. It should learn that the task runs quicker and adjust accordingly.
Maybe posting it on the PrimeGrid forum helps.
The problem is that BOINC adjust a project not a task, so if one task runs slow it thinks all other tasks run slow as well.
But normally it adjust as soon as a task completes.