At the beginning of the novel, George and Lennie are chased out of the town of Weed because Lennie "touched a girl". The townspeople do no even take the time to examine or question Lennie before they proceed to try to hunt him down and lynch him. If they had, they would have seen that he was mentally retarded and had no intention of hurting the girl. In addition, when Lennie and George take the bus to the new ranch they will be working at, the bus driver drops them off a long way from the ranch. It is obvious he doesn't want to have to go out of his way for a couple of "bindle-stiffs". Thus, they have to spend the night outside by the road and are late getting to the ranch. When they do get to the ranch, as mwestwood says, they are treated with a lot of questions and hostility.
The setting of "Of Mice and Men" is the time of the Great Depression in which so many men were out of work, a time in which there was tremendous competition for jobs. At this time, if anyone were the least questionable in reliability, capability, etc. he was immediately eliminated and someone else was hired as there was a superfluity of applicants for every job. And, because of this scrutiny of each applicant, men watched one another lest they lose their jobs. This competition for work caused suspicion and hostility.
In "Of Mice and Men," George and Lennie and the others represent these displaced men in search of employment. As a consequence of these people being estranged and insecure, the distrust and dislike among the itinerant workers is high.
Knowledgeable of the scrutiny that itinerant workers are under, George has Lennie stay with him outside of the ranch where they have been hired. When Lennie asks why they are not going to the ranch that has supper, George replies, "Tonight I'm gonna lay right here and look up. I like it." George wishes to stay beyond the boundaries of all the conflicts of being in a ranch house with strangers; he wishes to enjoy a last peaceful night. Added to this, if they arrive in time to go out and work, there are fewer chances of any conflict developing before they can prove themselves as good workers. Also, George has one more opportunity to instruct Lennie on how to behave around the other men; a fortunate opportunity as it turns out since Lennie has forgotten some of George's "rules."