Congruent triangle word problem

There are two tall trees they are 13 yards apart. Bob is walking from point B to point C along line BC.
After some time Bob stopped at point E he looked at the tip of both trees A and D. his site lines created a 90 degree angle and AB is 5 yards and AE is equal to DE. Bob walks at a rate of one yard every second. How long did it take for Bob to walk from point B to point E.