can I change the eta?

For those of us who have set goals with a certain time frame, can we reset the time we have given ourselves to meet those goals? Yes, I know I have come a long way and I am proud of what I have done. I set the goal to be 100 pounds less as a mini-goal and I just can't seem to reach it. Every time I have to post pone the mark, I get angry at myself for not not reaching it. Many things are running through my mind and I can't figure out why I just can't get there.