diff --git a/homeassistant/components/wwlln/config_flow.py b/homeassistant/components/wwlln/config_flow.py
index 35b6ce6c8a0..81992794d2a 100644
--- a/homeassistant/components/wwlln/config_flow.py
+++ b/homeassistant/components/wwlln/config_flow.py
@@ -60,11 +60,14 @@ class WWLLNFlowHandler(config_entries.ConfigFlow):
         else:
             user_input[CONF_UNIT_SYSTEM] = CONF_UNIT_SYSTEM_METRIC
 
-        # To simplify things, we don't allow users of the config flow to
-        # input a window; instead, we make a sane assumption to use the
-        # default (stored as seconds, since timedelta's aren't
-        # JSON-serializable):
-        if CONF_WINDOW not in user_input:
+        # When importing from `configuration.yaml`, we give the user
+        # flexibility by allowing the `window` parameter to be any type
+        # of time period. This will always return a timedelta; unfortunately,
+        # timedeltas aren't JSON-serializable, so we can't store them in a
+        # config entry as-is; instead, we save the total seconds as an int:
+        if CONF_WINDOW in user_input:
+            user_input[CONF_WINDOW] = user_input[CONF_WINDOW].total_seconds()
+        else:
             user_input[CONF_WINDOW] = DEFAULT_WINDOW.total_seconds()
 
         return self.async_create_entry(title=identifier, data=user_input)
diff --git a/tests/components/wwlln/test_config_flow.py b/tests/components/wwlln/test_config_flow.py
index 9751f5d5c9c..349dc19dce4 100644
--- a/tests/components/wwlln/test_config_flow.py
+++ b/tests/components/wwlln/test_config_flow.py
@@ -1,4 +1,6 @@
 """Define tests for the WWLLN config flow."""
+from datetime import timedelta
+
 from homeassistant import data_entry_flow
 from homeassistant.components.wwlln import CONF_WINDOW, DOMAIN, config_flow
 from homeassistant.const import (
@@ -36,12 +38,14 @@ async def test_show_form(hass):
 
 async def test_step_import(hass):
     """Test that the import step works."""
+    # `configuration.yaml` will always return a timedelta for the `window`
+    # parameter, FYI:
     conf = {
         CONF_LATITUDE: 39.128712,
         CONF_LONGITUDE: -104.9812612,
         CONF_RADIUS: 25,
         CONF_UNIT_SYSTEM: 'metric',
-        CONF_WINDOW: 600.0,
+        CONF_WINDOW: timedelta(minutes=10)
     }
 
     flow = config_flow.WWLLNFlowHandler()
@@ -88,7 +92,7 @@ async def test_custom_window(hass):
         CONF_LATITUDE: 39.128712,
         CONF_LONGITUDE: -104.9812612,
         CONF_RADIUS: 25,
-        CONF_WINDOW: 300
+        CONF_WINDOW: timedelta(hours=1)
     }
 
     flow = config_flow.WWLLNFlowHandler()
@@ -102,5 +106,5 @@ async def test_custom_window(hass):
         CONF_LONGITUDE: -104.9812612,
         CONF_RADIUS: 25,
         CONF_UNIT_SYSTEM: 'metric',
-        CONF_WINDOW: 300,
+        CONF_WINDOW: 3600,
     }