The GPG agent is actually gnome-keyring-daemon from the gnome-keyring package. You can change the defaults in dconf just like the other graphical GNOME applications.
From the description of /desktop/gnome/crypto/cache/gpg-cache-method:
The method to use for caching passphrases typed into the GPG agent.
Should be one of: 'always' caches permanently, 'session' caches until session end,
'idle' caches until the not used for gpg-cache-ttl seconds, 'timeout' caches until
gpg-cache-ttl seconds.
gcr isn't responsible.
The GPG agent is actually gnome-keyring- daemon from the gnome-keyring package. You can change the defaults in dconf just like the other graphical GNOME applications.
From the description of /desktop/ gnome/crypto/ cache/gpg- cache-method:
The method to use for caching passphrases typed into the GPG agent.
Should be one of: 'always' caches permanently, 'session' caches until session end,
'idle' caches until the not used for gpg-cache-ttl seconds, 'timeout' caches until
gpg-cache-ttl seconds.