In most areas of the world, there are moths. A lot of the moths that people see come out around early evening.
So when the poor man sends for Father Gilligan, it is early evening. Most of the people are asleep because this is before people were staying up late with electricity and such, but it is still not the middle of the night.
We can see this because as Gilligan sleeps, the moth hour ends and the stars come out. Later on, the moths come again when it gets to be a bit before dawn. That is when Gilligan wakes up.
W.B.Yeats' "The "Ballad of Father Gilligan" is a moving story of how God comes to the rescue of a sincere priest whose only concern is the salvation of the souls of his impoverished parishioners.
Father Gilligan who was exhausted in fulfilling his priestly duties day and night during an epidemic in the Irish countryside, either in giving the last communion to his poor parishioners who were dying in large numbers or conducting funeral services for them, was at home one evening taking a well deserved rest and had dozed off in his chair.
Yeats very poetically refers to the approaching twilight that evening as,
At the moth-hour of the eve
in order to emphasize the rural background of his ballad. The traditional ballads belonged to the illiterate rural folk and were passed on from one generation to the next by word of mouth. The poor illiterate villagers never possessed a clock or a watch and they always told time by the changes which took place from time to time in Nature.
In the Irish countryside, both at dusk and at dawn the countryside would swarm with moths. The villagers would ascertain that it was either dusk or dawn by the presence of the moths.
Just as Father Gilligan had dozed he was disturbed from his sleep by the urgent call of another dying parishioner. Wearily, Father Gilligan began to grumble and murmur about his lack of rest:
'I have no rest, nor joy, nor peace,
For people die and die;
But the very next instant he checks himself seeks God's forgiveness and kneels down by the side of his chair and begins to pray. However, shortly Father Gilligan is completely overwhelmed by sleep. Soon, it is night and once the stars appear in the sky the moths disappear,
And the moth-hour went from the fields.
The tired Father Gilligan slept the entire night kneeling down by the side of his chair. Early in the morning, at dawn he woke up to the cheerful sound of the chirping sparrows and once again the moths which appeared in the twilight reappeared at dawn:
Upon the time of sparrow chirp
When the moths came once more,
Poor Father Gilligan realized his mistake and rushed off to the house of the dying parishioner, only to be greeted by the dead man's widow with the news that he had actually come earlier on and had ministered the last communion to the dying man and by doing so had ensured the salvation of his soul:
The sick man's wife opened the door,
'Father! you come again!'
It is then that he realizes that God the Creator had taken pity on him who had worn himself out completely in His service, had sent an angel to minister the last communion to the dying man:
'He Who is wrapped in purple robes,
With planets in His care
Had pity on the least of things
Asleep upon a chair.'