There are lots of examples where something takes longer or is sped up based on our degree of faithfulness. For example D&C 105:1-13. When God changes His mind – if you can call it that – it is not in the same way that we imperfect mortals change our minds.
Great link: http://speeches.byu.edu/reader/reader.php?id=684
We change our minds all the time due to receiving more information than we previously had. He already knows everything so with Him, I think it is more like, He is prepared for every possible contingency, and frequently makes provisions for various possibilities … if this happens I will do this … if they choose this I will delay that … etc. Now, if there is a Deadline with a capital D, maybe it is set in stone and wont change no matter what. But most deadlines have at least some give and take to them, the main thing that can change them being our level of preparation and our choices.