Once the configuration option for TSA URLs is available, it should be possible for the user to en-/disable timestamping before exporting a file to a digitally signed PDF. Therefore a (checkbox) option shall be added to the "Digital Signatures" tab in the Export as PDF dialog, that allows to enable timestamps. The default should be off (disabled), and it should be possible to enable it only if at least one TSA URL is configured.
Part of Bug 84881 - Add RFC 3161 timestamp when digitally signing PDF (tracker) Status -> NEW Severity -> enhancement
Tor found a better solution: A select dropdown with TSA URLs, with timestamping enabled only if a TSA is selected. This will be in 4.5 (It's in nightly since about March 1st). Thanks for the excellent work!