DarkUFO says that the E! source is the correct one.
5:31 a.m.: Lost has no confirmed time slot for when it comes back next spring for season six. It will be on, for sure, they just don't know yet if it will air Wednesday at 9 or Tuesday at 10, etc.
At the ABC Upfront Presentation it was announced that Lost will return in 2010 on Thursdays at 8:00pm. Note this is of course subject to change.