Can I make the effects disappear after a certain period of time?
Yes. Each effect that has this feature will have a “Delay Timing” property, and an entry marked “(+) Fade-Out”. If you click that entry, then re-open the menu to Delay Timing, you will see three new entries:
Fade-Out When: After how many seconds to begin hiding the effect.
Fade-Out Duration: How long after beginning to hide the effect will it completely disappear
(-) Fade-Out: Click this to remove the fade-out for this effect.
Please remember that the time is relative to when you start the sim, not when the location (or effect) starts.