Timely redelivery is not always a condition of a time charterparty, but may well be an 'intermediate' term since a short delay in redelivery will not justify the termination of the contract.
Hyundai Merchant Marine Co Ltd v Gesuri Chartering Co Ltd (The Peonia),  1 Lloyd’s Rep 100, per Bingham LJ at p.108:
The owner need not comply with such [illegal] an order, because he has never agreed to do so. Alternatively, he may comply with the order although not bound to do so: if he does comply, he is entitled to payment of hire at the charter-party rate until redelivery of the vessel and (provided he does not waive the charterer’s breach) to damages (being the difference between the charter rate and the market rate if the market rate is higher than the charter rate) for the period between the final terminal date and redelivery. In the further alternative, if … the charterer’s breach is repudiatory, the owner may accept the repudiation, treat the charter as at an end and claim damages.