diff --git a/aurora/utilities/json.py b/aurora/utilities/json.py
index 3859bf4..b231b7b 100644
--- a/aurora/utilities/json.py
+++ b/aurora/utilities/json.py
@@ -14,7 +14,8 @@ class JSONEncoder(json.JSONEncoder):
             case datetime():
                 return int(o.timestamp())
             case timedelta():
-                return str(o)
+                from ..utilities.utils import timedelta_to_string
+                return timedelta_to_string(o)
             case AuroraBaseModel():
                 return o.dump()
             case Type():