There's not a term that I'd know of, but you'd have to know the time of year and the seasonal pattern for your latitude and which way's north before you could get an accurate of the time of day. How accurate do they need to be though? In a survival situation in the countryside you need to be very aware of the daily cycle (when night's going to fall, etc) but you don't need to know the exact time. If you're just looking for a word for this, then I wouldn't worry about it. Just describe your characters doing that. e.g. Jimmy held his hands up to the sun and counted two hand widths between the sun and the horizon. "We need to go now if we want to get back to camp before nightfall." (showing's better than telling for this kind of thing... if they do it a lot, you can just put it in dialogue... "six handwidths. We've got plenty of time." or similar.)
You can use shadows to follow the day's cycle (no need for a sundial but they're simple enough to build). You can determine the sun's angle in the sky by the shadow length. At the equator, if the shadow's a puddle at your feet it's noon. If it's the same length as the object it's mid morning or mid afternoon (halfway between sunrise and noon or halfway between noon and sunset. The direction of the shadow tells you if it's morning or afternoon (as long as you know the direction you're facing - and you can calibrate this by observing the sun over the course of the day). The further away from the equator you go the harder it is to do this because the position of the sun at sunrise, noon and sunset depends on the time of year, however if you know the seasonal patterns it can still be done. Stonehenge is thought to be a calendar/time measuring device, measuring the position of the sun at sunrise and sunset through the year.