Practical Completion [PC] generally occurs at the end of building works on site.
Although there is no legal definition of Practical Completion, it usually occurs when the building can be beneficially occupied by the Employer. PC triggers the release of the 1st moiety of retention, generally makes the Employer responsible for insuring the building, makes ends the contractors liability for liquidated damages, and starts the defects liability period.
Under JCT Contracts, they provide no definition of what PC is, leaving it to the Contract Administrator to use their discretion.
Unless prescribed in any of the contract documents [zero defects] the contractor will have a number of defects / snagging to attend to at PC.