nitpick: Superfluous comma: `The 3000 is used to check that it is not a year`

nitpick: Please move that comment past the `if (timestamp == NULL)` condition: ```c if (timestamp == NULL) { /* Neither timestamp, nor date property exists */ as_validator_add_issue (validator, node, "release-time-missing", "date"); } else { .... ```

The `hint` parameter should be the actual timestamp and not a "timestamp" string, so `as_validator_add_issue (validator, node, "release-timestamp-invalid", timestamp);`

You can drop the translator hint, there are no tag names here.

This arbitrarily checks for a "new enough" timestamp, it would be better to just check if the string value is a valid integer. Like this: ```c gint64 timestamp_int = 0; errno = 0; timestamp_int = g_ascii_strtoll (timestamp, NULL, 10); if (errno != 0 && timestamp_int == 0) as_validator_add_issue (validator, node, "release-timestamp-invalid", timestamp); ```