That's what keyframing is for, though effects with automatic built-in animation like ripple will be tricky to time correctly.
To control when the effect begins and ends, manually adjust the position of the keyframes for the effect on a specific layer.
1. In the composition window, below the Project window on the left of the screen, select/click once on the effect's layer to select the layer.
2. Hit the "u" key twice to reveal the keyframes automatically set by the effect.
3. There will be at least two set keyframes; select the key frame on the right of the first keyframe. Manually decrease or increase the interval between keyframes.
4.For the effect to end sooner, move the effect keyframe on the right to the left - decreasing while maintaining the interval.
- The above refers to AF CS (AF 8)
If you're new to AE, it really helps to get a solid foundation first. The resources linked on this page will cover the kind of stuff you're asking for and a WHOLE LOT MORE: Getting started with After Effects
Thanks for the help people. I will have a play around.