The workaround should not be needed as we know now the source of the original problem. It was NTP changing time more or less randomly as hosts were wrongly configured (for few years...)
Anyway the add_host script should block until host managed to synchronize the time and do not allow to enable it in ONE before that. All tier2 should depend only on hardware clock, which means NTP should be disabled.
- Make sure that NTP is disabled on every tier2.
- Make sure that NTP has finished synchronizing on every host before adding the host in Opennebula.