Investigate Work Time module.
Try building a time tracker using Flag and ECA.
Tried using datetime range for start/end time, but unable to create with only start value due to this issue:
https://www.drupal.org/project/drupal/issues/2794481
Smart date end date is also required: https://www.drupal.org/project/smart_date/issues/3489072
Workaround by setting end date to start time on initial creation.
Working ECA:
