Figure 9.70. Click the purple dotted line to edit a Linear Timewarp, not add another one.
You can edit a Linear Timewarp to tweak any of the settings you find in the Add Timewarp dialog, but make sure you're editing the filter and not asking Liquid Edition to add another Linear Filter on top of the one that already exists. Timewarp doesn't stack particularly well, which leads to strange results and possibly some green flashes on the screensomething you will be keen to avoid.
To edit a Linear Timewarp