aemet: fix forecast timestamp sensors

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

homeassistant/components/aemet/sensor.py

@@ -4,8 +4,10 @@ from __future__ import annotations
 from homeassistant.components.sensor import SensorEntity, SensorEntityDescription
 from homeassistant.const import ATTR_ATTRIBUTION
 from homeassistant.helpers.update_coordinator import CoordinatorEntity
+from homeassistant.util import dt as dt_util
 
 from .const import (
+    ATTR_FORECAST_TIME,
     ATTRIBUTION,
     DOMAIN,
     ENTRY_NAME,
@@ -130,4 +132,6 @@ class AemetForecastSensor(AbstractAemetSensor):
         )
         if forecasts:
             forecast = forecasts[0].get(self.entity_description.key)
+            if self.entity_description.key == ATTR_FORECAST_TIME:
+                forecast = dt_util.parse_datetime(forecast)
         return forecast