Help with the conditional probability in this problem

Question

The beacon of light from a prison turns on itself so it takes to light the same area 40 seconds. A prisoner organizing a prison break needing 27 seconds to reach and climb the wall. If the prisoner start a leak when choosing start hour randomly, ¿what is the probability that manages to escape without being seen?

Answer 1

$13$ out of the $40$ seconds of one period are fine, so ...

Answer 2

This is a very vaguely worded question. I am assuming that

(i) All points on the path the prisoner takes get lighted every 40s.

(ii) S(he) starts so that full use of the 40s is enabled.

With the above assumptions, P(not seen) = 1 if time for leak < 13s, and 0 if it is ≥ 13s.