The 'odd–even rule' means that between 8 a.m. and 8 p.m., only vehicles with number plates ending in odd numbers can drive on odd-numbered dates, and only those with number plates ending in even numbers can drive on even dates.
However, there are only three stanzas and three is an odd number, it's not in a pair, it's jarring and resembles the obstacles that prevent Agnes and Burns's love from being fated.