Make the test less picky.
Jenkins sometimes fail with error: ../tests/propertysystemtests.cpp(603): error in "testCreatePropertySpeed": difference{21.9529%} between static_cast(ts_create.toMicroSec()){819694} and static_cast(ts_get_set.toMicroSec()){1050256} exceeds 20%
E.g. http://dsjenkins.cloudapp.net/jenkins/job/dSS_MR/1407/console