You would probably use 'scenes' to accomplish this. Basically, you set Markers at the measure you want the effect to start and stop. Then, create and save a 'scene' with the effect turned ON, and reference that scene at the Marked measure. Remove the scene at the point in the song (measure) where you no longer want the echo (effect). You have to be careful with scenes. In the 'System' menu, you can choose WHAT you want affected in Scenes...things like EQ, Faders, Effects etc. If for example you leave the EQ choice ON, and then you save the scene, that scene contains whatever EQ settings are present at THAT TIME. If you subsequently change them after listening to the song etc, when that scene is called up, it will revert back to the settings at the time of the SAVE. Scenes work great, but you just have to be careful that you know what is saved IN them. Or, you can turn off the items you DON'T want saved with the scene. When I first got the machined, I tried to use them a LOT. I have learned to use them very sparingly.
Steve