Sure. This is to get the next nearest Tuesday, Thursday or Saturday (whichever is saved in extra.new_week_day) after the ``push_start_date``. Let's assume they are 'Tuesday'

Days are numbed: 0 - 7 for Sunday to Saturday (because javascript :P).
``day_index`` - the day of the week of the ``push_start_date``
``new_week_day_index`` - the day of the week of 'Tuesday' (Tuesday's is always 2)

``days_till_start`` calculates how many days to add to ``push_start_date`` to get to the next 'Tuesday'.