Ive done about 3 transmissions changes in my time, but normally taking it out and reinstalling. I can drop a auto trans in about an hour, 2 hours when I was pulling my first 5 speed because their was more involved (removing the shifter). Takes about 3 hours to reinstall an auto trans, and about the same time for a manual. I would suspect you can get it done in about a full day or two. Just make sure you grab all the needed electronic parts for the auto trans.

Richard E
1989 Montero - Stock-ish
1989 V6 Auto Raider - 5.3 Vortech Swap.
1987 Mitsubishi Starion 2.6t, soon to be 3.5
1983 Honda XL600R