Art. 33 CISG
The seller must deliver the goods:
(a) if a date is fixed by or determinable from the contract, on that date;
(b) if a period of time is fixed by or determinable from the contract, at any time within that period unless circumstances indicate that the buyer is to choose a date; or
(c) in any other case, within a reasonable time after the conclusion of the contract.
The Secretariat Commentary on Art. 31 of the 1978 New York Draft, predecessor to Art. 33 CISG, gives insight into the drafters' unterstanding on the eve of the 1980 Vienna Diplomatic Conference.
Overview of case law on Art. 33 CISG: UNCITRAL Digest
The UNCITRAL Digest on the CISG can be used as a starting point to discover the relevant case law on this article.