Regulations Governing the Licensing of Images and Publications of the National Palace Museum Article 8

In principle, negatives or digital files of images from NPM may not be loaned for more than three months. However, if an application for an extension is filed within 30 calendar days before the expiration date and is approved by NPM, the loan period may be extended for only once for one month.
中文原文 國立故宮博物院藏品圖像授權及出版授權利用辦法第8條
本院藏品圖像底片或數位圖檔借用期限以不超過三個月為原則。
但申請人於到期前三十個日曆天內以書面提出申請延長,並經本院同意者得依約延長,延長次數以一次一個月為限。

English translation for reference only; the Chinese text prevails. Not legal advice.