How to identify digitally signed document's exact signing time
In Estonia the document signing time is considered to be the moment when a validity confirmation query for the certificate used for digital signing is made (OCSP responce aka validity confirmaton time). In the digitally signed document data it will be marked as UTC time.
Developers of digital signing applications or services with digital signing support should consider that the timezone in the digitally signed document is UTC and make the necessary conversions for displaying signing time.
Starting from DigiDoc3 client version 3.8 the digital signing time is displayed throughout according to the same rules. List of changes made to 3.8 version can be found here.
NB! Older versions of DigiDoc3 software (3.7.2 and older) calculate the digitally signed documents signing time from UTC time. Computers usually show time according to their current timezone configuration in relation to Greenwich time. DigiDoc3 client desktop software takes into consideration the computers timezone settings and then calculates the displayed signing time.
Because of these specifics it's possible that DigiDoc3 client displays the signature time with hourly difference depending if the signing was done during Estonian winter time (UTC +2) or summer time (UTC +3). If your computer has some other non-Estonian time zone configured while checking the signature with DigiDoc3 client then it's possible that the variations in signing time are different.