The early morning and late afternoon is the best time to take outdoor pictures, including backyard landscape pictures. Many photographers believe up to three hours before the sun rises is best for outdoor photos as the sun is lower and provides a good color palette.
During the late afternoon, just before the sun sets, the sun is also at a low point. This is another good time to take outdoor photos. This time provides less contrast and not as much harsh light. For afternoon photography of a backyard, take the pictures up to a couple hours before the sun sets.