Thank's for your replay Alec, but I'm referring to the timeline animations and your answer addressed frame by frame animations.
Say, I wanted to insert 24 frames (i.e. 2 seconds in my case) at the 5 second position. The only way I can think of is extending the duration of the animation (thus adding frames at the end) and moving all key frames right of the insertion point on all layers . Although I can select multiple key frames at a time, it is a very tedious prosess, especially if the animation cannot fit on one screen.
Is there any way to insert frames anywhere else than at the end?
PS! I tried to include a screenshot, but it was removed when I hit the Post button.
As far as I can tell it is not possible to do this. Photoshop's video capabilities aren't exactly on par with http://www.adobe.com/products/aftereffects.html, which might be more suited to your needs if this is a big problem.
I know your pain as I have had to do it the manual way when pre-composing an animation. It takes a long while, but it made me realise that it is better to just animate in After Effects if you have the program.
If you aren't familiar with the product, or are a bit rusty, you should take a look at the Learn After Effects show on Adobe TV. It has some great tutorials for you to look at: