How do the time bars in clause 61.3 operate?

Clause 61.3 provides that, for certain compensation events, if the Contractor does not notify them within 8 weeks of becoming aware of them, it will lose the right to a change in the total of the Prices and the contractual Completion Date. That doesn’t sound very much like mutual trust and co-operation, does it ? Is it appropriate to have time bars in this contract and do they work ?