mdbess wrote:...... I want some frames to be longer and others to be shorter ....
You have to think outside the box. Find a common multiplier for the frames and then duplicate those that you want to be longer than others.
For example let us say you have 5 frames and you want them to be displayed for the following number of seconds.
Frame A 1 second
Frame B 1 Second
Frame C 2 seconds
Frame D 1 Second
Frame E 2 seconds.
What you would do is duplicate Frames C and E and place them on the time line as