If the ground has not been tilled, and your area is not some kind of unusual, there will be more deer in the field more often then when the beans are standing; especially when the field has just been harvested or is being harvested. Very early morning and starting just before sundown...much earlier if the field is secluded.

They will sometimes stay and meander around in the harvested field for lengthy periods as they pick the loose beans off the ground.

Find the trails they commonly use to enter/exit the field.