diff --git a/app/main.py b/app/main.py
index 5a9d729..dfe0db0 100755
--- a/app/main.py
+++ b/app/main.py
@@ -43,9 +43,15 @@ async def get_test():
 
 
 @app.get("/download/")
-async def download_grib(background_tasks: BackgroundTasks):
-    """Download and process GRIB files into csv of requested parameters"""
-    background_tasks.add_task(service_grib.extract_useful_data)
+async def download_grib(
+    background_tasks: BackgroundTasks,
+    target_time: str = None,
+):
+    """Download and process GRIB files into csv of requested parameters
+
+    :param target_time: well formed ISO 8601 time string, we will try to download GRIB available just before it
+    """
+    background_tasks.add_task(service_grib.extract_useful_data, target_time)
     return JSONResponse(content={"status": "Background task started"})
 
 
diff --git a/services/grib/service.py b/services/grib/service.py
index b6ddb20..08072f4 100644
--- a/services/grib/service.py
+++ b/services/grib/service.py
@@ -117,12 +117,17 @@ class Grib:
         )
 
     @staticmethod
-    def extract_useful_data():
+    def extract_useful_data(target_time: str = None):
         """Download and process GRIB files into csv of requested parameters
 
+        :param target_time: well formed ISO 8601 time string, we will try to download GRIB available just before it
+
         :returns: filenames of the resulting csv
         """
-        target_time = Grib.fresh_grib_time()
+        if not target_time:
+            target_time = Grib.fresh_grib_time()
+        else:
+            target_time = Grib.fresh_grib_time(datetime.fromisoformat(target_time))
         save_to = f"{target_time.strftime('%Y%m%d')}-{str((target_time.hour // 6) * 6).zfill(2)}.csv"
 
         for forecast_hour in range(MAX_FORECAST_HOUR):