For deadlines i use a week based paper calendar and setback can be handled by negative time entries, like:

  01.15-00.00 refund for issue 6789 (75mins)

It's not ideal but it barely happens.

Another minor issue is that my parser currently does not support overnight shifts like

  2022-11-15
  - 23.45-01.18 another task

These have to be divided into 2 separate ones:

  2022-11-15
  - 23.45-23.59 another task
  
  2022-11-16
  - 00.00-01.18 another task