The structure will go into its final reinforcement phase which will occur on the day and time selected by the owner.
This timer will be at least 5.5 days in highsec, 2.5 days in lowsec and nullsec, and 0.5 days in wormhole space.
If the structure is in High Sec and it goes into its final reinforcement timer, then 5.5 days must pass PLUS as long as it would take before the day and time selected by the defender comes to pass, plus or minus up to two hours.