Due to strange yaml behaviors begin/end times can be strings

harvester/endpoint/opensearch.py

@@ -190,10 +190,20 @@ class OpenSearchQuery(Query):
         url = urls[mimetype]["url"]
         queryables = urls[mimetype]["params"]
 
+        if isinstance(self.time_begin, str):
+            time_begin = self.time_begin
+        else:
+            time_begin = self.time_begin.isoformat()
+
+        if isinstance(self.time_end, str):
+            time_end = self.time_end
+        else:
+            time_end = self.time_end.isoformat()
+
         mapping = {
             "{geo:box}": self.bbox,
-            "{time:start}": self.time_begin.isoformat(),
-            "{time:end}": self.time_end.isoformat(),
+            "{time:start}": time_begin,
+            "{time:end}": time_end,
             "{count}": int(
                 next(
                     param["maxInclusive"]