If you took enough you should feel it within 20 minutes. Enough is different for everyone so start low and Build it up!

1st day for me. Take it slow though, because before you know it you might be thinking your having a heart attack!

It has a relatively long half life so I wouldn't expect to feel it for a day or so. I don't really "feel" it unless I'm taking heavy doses (150 mcg. + per day).

Just to add to his question, and touch on what I think he is asking, how long until you notice the affects as in weight loss and lookin leaner also.

Too many variables in this question to give you a definitive answer. Depends on where you are starting out in terms of muscle mass and bodyfat, as well as your diet/training. You will begin burning more calories right away but it depends how much of a total calorie deficit you are in on how long "noticeable" results will take to materialize.