#399

backend/app/services/post_import_previewer.rb

@@ -1,3 +1,4 @@
+require 'time'
 require 'timeout'
 
 class PostImportPreviewer
@@ -86,7 +87,8 @@ class PostImportPreviewer
 
     if row[:metadata_url].present? && row[:metadata_url] != url_for_metadata
       clear_automatic_values!(attributes, provenance, tag_sources)
-      clear_fetch_warnings!(field_warnings)
+      field_warnings = { }
+      base_warnings = [ ]
     end
 
     if validation_errors.blank? && normal_url.present? && existing_post
@@ -248,7 +250,8 @@ class PostImportPreviewer
   def sanitise_metadata_time value
     return nil unless value.is_a?(String)
 
-    Time.zone.parse(value)&.iso8601
+    time = Time.iso8601(value)
+    time.nsec.zero? ? time.iso8601 : time.iso8601(9)
   rescue ArgumentError, TypeError
     nil
   end