Hi
If you are adding an effect to the video as a unit and not just a shorter clip it will take some time to render and it would affect the whole timeline. Shortish clips (30 seconds or less) generally render as you make the changes to the keyframes and can usually be played through quite quickly.
If the effect you have planned is acting only on a small length of video, just split it off and add the effect to that section.
It can be useful to place the processer % usage graph from the task manager on the screen as you can see at a glance whether your PC is working overtime.

When it drops back to 1-2% you know rendering is complete even when the green bar is not visible.
Nat