Not a countdown clock
A maximum tolerable period is a planning boundary, not permission to wait until the last minute before responding.
Evidence
Contracts, regulation, customer commitments, inventory, cash flow, safety and operational consequences can inform the threshold.
Uncertainty
The exact point may be a range rather than a precise hour. Document assumptions instead of manufacturing false precision.
Strategy link
Recovery objectives should normally sit comfortably inside the point at which impacts become unacceptable.
Business continuity is organization-specific. Recovery priorities, legal duties, safety requirements, contracts, insurance terms and technical recovery methods should be validated by the responsible people in the organization.