Timely, punctual and continuous payment of hire in advance is a primary obligation of the charterer and also an absolute one which, as Lord Wright said in The Petrofina  2 All ER 939 at p.946, is not excused by accident or inadvertence.
Per Crane J. in Hyundai Merchant Marine Co. Ltd. v Furness Withy (Australia) Pty (The Doric Pride) EWHC 945 (Comm) at para 16:
… it is clear on authority that, in the context of a charter-party, a vessel is detained when, as a result of some geographical or physical constraint upon her movement, she is prevented from proceeding as directed under the charter-party. If there is some physical or geographical constraint on a vessel’s movement which prevents her from proceeding on the course directed by charterers, the fact that she is not prevented from proceeding elsewhere does not negate "detention". As Mr. Justice Kerr held in The Mareva A/S  1 Lloyd’s Rep. 368, when considering the meaning of "detention by average accidents to ship or cargo" in clause 15 of the NYPE form:
I think that it is intended to refer to some physical or geographical constraint upon the vessel’s movements in relation to her service under the charter.[page 382]
Thus whether or not the vessel’s movements are confined depends upon her ability to proceed as directed under the charter, not upon her freedom of movement in a less specific sense.
In ST Shipping and Transport Pte Ltd v Space Shipping Ltd (The CV STEALTH)  EWHC 880 (Comm) per Popplewell J. at para 33:
Clause 28 makes no reference to voyage orders, but merely to the undertaking of a voyage. If the increased risk materialises in the course of a voyage, the clause comes into effect irrespective of whether it arises subsequently to the original voyage orders. In the analogous circumstances of safe port warranties in time charters, the contractual promise is a continuing one, such that if a port is prospectively safe when the order to proceed there is given, but becomes unsafe at a time when a time charterer could give a fresh order in time for the vessel to comply with it and avoid the unsafety, the time charterer is in breach of the warranty: see Kodros Shipping Corporation v Empresa Cubana de Fletes (The "Evia" (No 2))  2 Lloyd’s Reports 309 per Lord Diplock at 310 and per Lord Roskill at pp. 319-320. Similar principles apply to clause 28 of the Shelltime 4 form. If the vessel is ordered to a port at a time when there is no materially increased risk of capture or seizure, but such a risk arises whilst she is en route, clause 28 would entitle the Owners to refuse to continue to comply with the order, if they were aware of it; and in the event of continued compliance, the charterers would be in breach of clause 28, provided that the risk arose before it became impossible for the charterers to give fresh orders which could be complied with in time to avoid the risk. It is common ground that breach of clause 28 does not depend upon any knowledge of the increased risk on the part of the Charterers: see Ullises Shipping Corp v Fal Shipping Co Ltd (The "GREEK FIGHTER")  EWHC 1729 (Comm) at paragraph 286.