It depends on how you define "clock." Is a sundial a clock? Essentially, a sundial is just a stick in the ground in a place where it can cast a shadow all day long. All the sundial adds is a set of marks showing where the shadow will be each hour of the day.
If you put a stick in the ground, I would not call that a clock. If you start adding marks on the ground for each hour of the day, you have started building a clock. You can do this experiment easily.
At night, it becomes harder, because the stars do not cast discernible shadows. However, if you are in the northern hemisphere and can find the start Polaris (the "North Star") and memorize the pattern of stars around it, you can tell the time of day (or night) in a fashion similar to the sundial, only using the position of one of stars near to Polaris, measuring its relative up/down/right/left position. There is a constellation there, Ursa Minor (the "Little Dipper") that forms an easily recognizable pattern. These are all terms you can do a web search on.
I found a site in the UK that has some fairly sophisticated projects for making a sundial, see the link below.