Gross and Effective time from an array of time DateTime objects

main.rb

def task_overalltime(timelines)
    array = timelines.split(',').map{ |x| x.to_datetime}
    nd_time = array.length.even? ? '' : '+'
    array = array.reverse
    rec_difference = 0
    array.each_with_index do |val, ind|
      if ind.odd?
        next_ind = ind - 1
        rec_difference = rec_difference + (val.to_time - array[next_ind].to_time).to_i.abs if array[next_ind].present?
      end
    end
    effect_time = get_effective_time(rec_difference)
    gross = time_diff(array.first.to_time, array.last.to_time)
    return "Gross Time : #{gross}#{nd_time}  Effective Time: #{effect_time}#{nd_time}"
  end

  def get_effective_time(seconds_diff)
    hours = seconds_diff / 3600
    seconds_diff -= hours * 3600
    minutes = seconds_diff / 60
    seconds_diff -= minutes * 60
    seconds = seconds_diff
    "#{hours.to_s.rjust(2, '0')}:#{minutes.to_s.rjust(2, '0')}:#{seconds.to_s.rjust(2, '0')}"
  end

  def time_diff(start_time, end_time)
    seconds_diff = (start_time - end_time).to_i.abs
    hours = seconds_diff / 3600
    seconds_diff -= hours * 3600
    minutes = seconds_diff / 60
    seconds_diff -= minutes * 60
    seconds = seconds_diff

    "#{hours.to_s.rjust(2, '0')}:#{minutes.to_s.rjust(2, '0')}:#{seconds.to_s.rjust(2, '0')}"
    # or, as hagello suggested in the comments:
    # '%02d:%02d:%02d' % [hours, minutes, seconds]
  end