First of all, stop comparing him to his older brother; I can see already that that isn't working for you just by the way you're praising your older son. I have four boys and EACH and EVERYONE OF THEM have their unique personalities and styles.
Why not make a game out of it? I bought posterboard and and made columns for each day of the week. I bought a whole lot of stickers from stars to shapes to superheroes. I would set a value; for example, for 1-10 stars, he would get a 'treat' within a certain price range. The more stars, the higher the value. I would either go to the dollar store or dollar general. I might even make it Chuck E Cheez or out for ice cream. My son is now 11 and has gotten "into the habit" of doing what he was supposed to. What is great is that because he's older, he doesn't want any rewards; he says that's for litle kids or babies. Get where I'm going with this? :-)
My son had this problem when he was about 7 or 8. I did and/or thought the whole "why can't you/he be more like Kenneth" but that was just not fair to him or his brother because it made him resentful of his brother and he would just do MORE to be 'different' from his brother, which wasn't a bad thing BUT, it was all negative.
I hope this helps and good luck to you and your family with this.
P.S. Also, the timer thing is just putting too much pressure on him; make a game of it instead. Act like you're going to do it woth him; "Let's see who can put their PJs on quicker; you or me?" And make the reward something like stay up an extra half hour on the weekend instead, or you he gets to pick the movie the family will watch together.
I have more 'reward' ideas if you'd like to hear them; send me a message.