Using app for backing tracks. How long can each track be??

Trying to use this app for backing tracks in a live set. How long can the imported audio files be in the audio recording section of the app? Our set is 45 min long, and has 4 tracks playing simultaneously non-stop throughout the whole set.

Trk 1. Click

Trk 2. Guitars

Trk 3. Bass

Trk 4. Samples

Main reason we need all 4 separate tracks playing simultaneously, is because we need to be able to adjust the audio levels of each track suited to the venue. Nothing more. If there is a better way to do this or a different app that could be suggested it would be greatly appreciated!!

Appreciate the support.

Thanks!