The time difference between the first plane hitting the North Tower and the collapse of the South Tower was 56 minutes.

Here's the breakdown:

* 8:46 AM - American Airlines Flight 11 hits the North Tower.

* 9:03 AM - United Airlines Flight 175 hits the South Tower.

* 9:59 AM - The South Tower collapses.

Therefore, the difference between the first plane hit and the South Tower collapse is 56 minutes.

It's important to note that the North Tower collapsed 47 minutes later, at 10:28 AM.