Slipping Trans

This is just some of the seals getting crispy and old and/or the torque converter draining down overnight. You can put off doing anything about this non-critical situation for a long time (at least until the weather's warm) by shifting out of Park and into Neutral before you start up the car first thing in the morning. By the time you've fastened your seat belt, turned on the radio, adjusted the mirror and all that, the torque converter will have filled up and Reverse engagement should be much more immediate.

Be sure your handbrake works or get into the habit of putting your foot firmly on the brake pedal if you do it this way.