Formation of a time charterparty, same as a voyage charter, governed by the ordinary rules of the law of contract, i.e. there must be an offer and acceptance, then the parties must have agreed all the essential terms either in writing or verbally to make the contract binding.
In Asty Maritime v. Rocco Guiseppe & Figli (The Astyanax)  2 Lloyd’s Rep 109 per Kerr LJ at pp.113 and 114:
We therefore conclude that the course of the negotiations in the present case shows perfectly clearly that the understanding and intention of both parties was that Mr. Panagiotis would conclude a head time charter with the registered owners and that it was on this basis that he would appear in the sub-voyage charter with the charterers as ‘disponent owner’.
… The description of Mr. Panagiotis as ‘disponent owner’ was admittedly in itself neutral. But the surrounding circumstances and the course of the negotiations clearly show that the intention was that he would conclude a time charter with the registered owners and that it was on this basis that he was described in the sub-voyage charter as ‘disponent owner’. This was inconsistent with his contracting in the capacity of a mere agent on behalf of the registered owners, with the result that they cannot contend that they were in fact his undisclosed principals.