https://developer.adobe.com/document-services/docs/assets/5b15559b96303194340b99820d3a70fa/PDF_ISO_32000-2.pdf has date format D:YYYYMMDDHHmmSSOHH'mm and includes this example and note:

For example, December 23, 1998, at 7:52 PM, U.S. Pacific Standard Time, is represented by the string:

D:199812231952-08'00

NOTE PDF versions up to and including 1.7 defined a date string to include a terminating apostrophe.
PDF processors are recommended to accept date strings that still follow that convention.

Contrast with PDF 1.7 format at https://opensource.adobe.com/dc-acrobat-sdk-docs/pdfstandards/pdfreference1.7old.pdf being D:YYYYMMDDHHmmSSOHH'mm':

For example, December 23, 1998, at 7:52 PM, U.S. Pacific Standard Time, is represented by the string

D:199812231952−08'00'