Which type of irony is being used in this piece of text?

"Unfortunately, the discovery was almost always made on
a Sunday. Thus a whole day was lost before the machinery of
pursuit could be set in motion. The posters offering rewards
for the fugitives could not be printed until Monday. The men
who made a living hunting for runaway slaves were out of
reach, off in the woods with their dogs and their guns, in
pursuit of four-footed game, or they were in camp meetings
saying their prayers with their wives and families beside them."