Please give us some more information in order to solve your problem:
-what configuration(processor, ram, operating system) has the computer on which you are running Tunebite?
-are these 30 seconds missing from every song you converted, and if so, is the gap happening in the same position(beginning, middle, end of the song) ?
-what format are the files you are converting(iTunes, wma, etc)?
-what version of registered Tunebite are you using ?