What is happening is you are getting the bezier curve and that can be confusing to deal with. After you are done with your mask you need to go frame by frame and adjust your mask points as needed to make it as neat as possible. This is very time consuming and when you do the math you will see why. You’ll sometimes want to only select one anchor or maybe the whole mask. You can do either by right clicking on the mask and then selecting the “ENTIRE MASK” or just an “ANCHOR”. Once you have selected either you can use your arrow keys to move them easily. You’ll have to do this anytime there is movement or change in shape. Select feather for both in and out in the properties as well to help give a more blended look. Play with the settings to get the look you want.
Now for the math…30 Frames per second=1800 per minute. Times that by the total time and you can quickly see how long it can take. Now of course if there is not much movement it will be much less but either way if you want it to really come out well you have to spend the time. Or buy some extra software to help..
Joe