I think dogs have some understanding of time, such as certain things happen at certain times of the day. But I think their view and experience of time is very different. Based on what I've read I would guess their time is made up of smells, sites and sounds. For example, 6 o'clock might be "the sun is setting and the air smells like exhaust from all the people commuting home" while 7 o'clock might be "sun is set, the air smells like food, my people are home" etc. By the changes in sunlight, in smell and sounds a dog might hear outside they are obviously capable of figuring out when things are likely to happen in a day.