Modern tanks do travel at 50MPH. But this is not Call of Duty or any other video Game. If the lead tank, takes off at 50MPH, no one will be able to keep up with him. The Queen's Lancers will be able to kill each tank one by one as they come through the 1K zone. The reason they travel at a slower speed is to increase unit integrity, cohesion and so that they can support one another if they do get surprised on the road heading west.

Once the tanks get into a firefight a T-72 might need to "sprint" forward or laterally in order to cover a flank or take advantage of a penetration. Since they are using Bound and Overwatch movement tecnhique, a tank will sprint forward to a covered position and sit still, watching for enemy vehicles while a platoon mate advances. The three tanks in the platoon would take turns leapfrogging forward once enemy contact is suspected. If they just ride all willy nilly, hanging ten, letting the breeze blow through their hair, they will get killed. I guaran-God-damn-tee it as a matter of fact!

As far as at what time during the advance they are detected? Well that would be as soon as they depart their bases. It would not be once they cross the 1K zone into West Germany. There are plenty of East Germans working for the BRD government to keep NATO informed.