refactor: to timezone specific datetime helper to avoid use deprecated functions

[bednar]

Closes #603

Proposed Changes

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• pytest tests completes successfully
• Commit messages are conventional
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.41%. Comparing base (550ff26) to head (1b7d42a).

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #652   +/-   ##
=======================================
  Coverage   90.41%   90.41%           
=======================================
  Files          39       39           
  Lines        3505     3505           
=======================================
  Hits         3169     3169           
  Misses        336      336           

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