Shouldn't be long, its normally around Easter.
The park hours are up to the w/c 16th Sept so far on the Disney website so keep an eye on the MK opening times.
Tickets should officially go on sale around May 1st. But you should be able to guess some of the dates before then if they are not released. When park hours for September and then October are released any day that has MK closing at 7pm is a good bet that its a party night.