Sorry for being so obtuse. We’re dealing with a lot of dimensions here, and it’s hard to explain that we mean "Halfway in time" as opposed to "halfway in space". Bear with us.
Anyway, so now you should have three Nodes making a path.
one node at 0:0, one at 4:0, one at 8:0.
Now of course I don't know what yours looks like. but I hope it looks like 2 straight lines.
Play this. the camera moves forward, slows down at the 4 second mark, then starts back up again. The reason it slows down is because that second node at 4 seconds has no velocity. Lets fix that.