Good question.

EA don’t announce their updates more than a day or two in advance. However, they have updated the game sometime in the first couple of weeks of the month every month since September.

Update: The Valentine’s Day update on January 31 didn’t contain Level 26 (although it did contain lots of cool stuff). It looks like Level 26 won’t be with us until March.

Further update: The large in-game update on February 1/2 has started rumors about level 26 being available sometime in the week of February 4. EA are unlike to say anything until it happens, so if there is something before March, be pleasantly surprised.