That makes perfect sense. When you're moving back into the past, you're talking from your perspective about your perspective. But when you're talking about a d

That makes perfect sense. When you're moving back into the past, you're talking from your perspective about your perspective. But when you're talking about a deadline, you're talking from your perspective about a "stationary" event in the future. Since you are moving forward, but the deadline stays in place, relatively speaking the deadline moves towards you - so you push it back, in its reference frame, into your future. If this sounds complicated, blame the fact that we use spatial intuitions for timekeeping. For instance, if you compare "step back" to "push back" in a spatial sense, they also mean opposite things, and for the same exact reason.