Is there an easy way on a Mac to split an audio file at defined intervals?
Use ffmpeg.  It's available via Homebrew and MacPorts, but I just prefer to use the prebuilt binaries

Just off the top of my head, you could do something simple like:

$ ffmpeg -i source_audio_file.mp3 -ss 0 -t 120 segment_1.mp3
$ ffmpeg -i source_audio_file.mp3 -ss 120 -t 240 segment_2.mp3
$ ffmpeg -i source_audio_file.mp3 -ss 240 -t 360 segment_3.mp3
.
.
.


To put this into a script wouldn't be too hard