Is it just the one task that the timer faults out on or are there other characters/tasks?
Things you can try at your end:
Store Springfield Elementary in your inventory then place it back in to your town to reset Skinner.
Activating the task by selecting it through the task bar rather than through the character menu/by clicking on Skinner directly.
Have Skinner start the task and the timer to say the duration left to complete the task, wait a couple of minutes so you know it's counting down then go to Krustyland or your friend screen to synch the game on the servers.
Try the steps outlined here
There are a lot of issues with the current update so if you're still having problems after the steps above then you may want to get in touch with EA via http://help.ea.com/contactus to have them look in to your game for you.
