Mat 20:3 And he went out about the third hour, and saw others standing idle in the marketplace,
Mat 20:4 And told them; Go also into the vineyard, and I will give you what is right . And they went their way.

The third hour means three "hours" after sunrise in the system of antiquity, but these "hôra" were not all of equal length. Instead, they were the hours of daylight divided into twelve equal parts, longer in the summer and shorter in winter. The assumption here is that this is three such periods after the first workers went out to work.

Note that the owner of the vineyard is not hiring just because he needs more workers. The cause mentioned is that the people were standing idle, doing nothing. There is a strong sense here that everyone should have work to do, that they should be producing something of value with the time.

The agreement here is only to work for "what is right." The word used means what is normal or expected. Since a denarius was a days

"Idle" is from argos, which means "not working," "not doing," and "idle." It was something of a critical term with the sense of "lazy."

"Marketplace" is from agora, which means "an assembly," "place of assembly," and "marketplace." "Public speaking" meant speaking in the marketplace.

"Right" is from dikaios, which means "observant of custom," "civilized," "righteous," "well-balanced," "lawful," "fitting," and "normal." It is usually translated as "righteous" or "just" in the New Testament, but the standard is doing what is expected and fair.