Trim the layer's in point until the animation is supposed to begin. You can always move the effect to a different layer if it's currently on video. Just make sure the other layer (a solid, probably) is the precise same H&V resolution and pixel aspect ratio as the video layer.
Use a solid as a track matte for the Write-On layer. Again, this won't help much if this effect's on a video layer right now. You'll have to move it to a solid.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA