Once you positively identify where you are, by a river/road crossing, or a town, jot down the time.
No! work out how long it will take to get there from the last turning point and write that on the map before you go. When you get there, compare the time on the map with the time on your watch and correct the ETA and track if necessary. No bl...y use writing the time when you get there! DR is the calculation of the unknown from the known.