You don't need to take pics. What you want is to use the pictures you have already shot and make the clip longer using those pictures. The thing is that every single frame has a predetermined length, because you work with a set number of frames per second. In order to make clips shorter or longer, you will need to add or subtract frames from the clip. As people have suggested, this can be achieved by taking more frames while animating.

However, when you're already in the next stage (which is editing), you cannot simply shoot some extra frames. Instead, you can "loop" frames; you just put the one same frame and put it a number of times after each other, extending the clip. Of course, it's important that you don't loop the wrong frames: you can generally only loop frames where there is no movement to prevent jerkiness.

So there you have it: just copy and paste frames you've already shot after each other as many times as possible.

EDIT: Alternatively, you can slow down or speed up part of the clip to match it to a certain time range. Note that this can and will create some jerkiness. But you can particularly get away with this technique when you use it in shots of just dialogue. This is how Keshen edits some of his shots.