You can expect about 2 hours or so groundschool for both combined. More time in classroom = less time in air = less £££. Emergency touch drills can be practised in the airframe, on the ground prior to flying.
Some instructors treat it as a type conversion. This is not the case, the differences training will allow you to fly VP prop (multi lever) & retractable u/c on aircraft with different systems. It will not be type specific to the PA28R, and this must be catered for in the training. Two examples that come to mind are Russian beasties with pneumatic systems and the Gardan Horizon with a hand crank.
The actual flying should normally be only an hour or two at most, in order to teach the subject to a current and competent PA28 PPL, most of which will be emergency drills. Whether the student is then competent to fly solo on type will depend on ability, irrelevant of the differences training.