Attempt to stabilize the test.

The "window" used by FewSecondsScheduler of 2.4s
was too narrow, and probably made possible to
finish the iteration, while test would wait
for max 11 executions (but due to window 0, 1 or 2
executions were more likely).

Anyway, as the UT is time limited (with the for cycle),
widening the schedule is not a problem, as it will
be detected anyway (will not run forever)