add auto centre diff and correct time estimate on stxm

[Relm-Arrowny]

Fixes #9 #61

Instructions to reviewer on how to test:

1. Run and check tests make sense.
2. Confirm tests pass

Checks for reviewer

• Would the PR title make sense to a user on a set of release notes

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (9d72da7) to head (fe6f0d5).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #63   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           25        25           
  Lines          579       612   +33     
=========================================
+ Hits           579       612   +33     

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