You don't necessarily have to add the Marker Ranges whilst recording. You can go through afterwards and quickly add just single markers at the start of each new slide. Once you added all the markers just add a single extra one at the end. Then in the Markers List you can select all Markers and convert them into Ranges using the Comb icon. Then you can use the Export Selected Marker ranges to Individual Files to split them up into individual .wav files. Then you can use the Batch process to convert them all to .mp3 files.
In fact you could speed up the process even more by saving your Normalization and NR settings as a Favorite. Then you can select that Favorite in the Batch Process and do all the processing and conversion to .mp3 all in one step.