Fix API use error message

csppfetch/__init__.py

@@ -693,7 +693,7 @@ class Downloader:
         if oldest_usable < timedelta(days=0):
             raise ValueError(f"oldest_usable should be positive; it is {oldest_usable}")
         if epoch_start > IMPLAUSIBLY_DISTANT_FUTURE:
-            raise ValueError(f"oldest_usable should be positive; it is {oldest_usable}")
+            raise ValueError(f"epoch_start should be less than {IMPLAUSIBLY_DISTANT_FUTURE}; it is {epoch_start}")
 
         self.name = name
         self.package_env_id = package_env_id