What is the maximum length Spin It Again can record?

Spin It Again is limited to recording 3.38 hours of audio at CD quality.

However, you can change the sample rate and other factors to get more recording time. (IE: you are recording an 8 hour book on tape.) 
Max Time  Format  
62 minutes  192,000 hz, 24 bit, stereo  
124 minutes  96,000 hz, 24 bit, stereo  
6.76 hours  44,100 hz, 16 bit, stereo  
13.52 hours  22,050 hz, 16 bit, stereo 
54.1 hours  11,025 hz, 8 bit, stereo 

You can change the recording format in the settings, by clicking "Settings". Click on the "Recording" page and change the settings to the appropriate values.