diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index b197b58e80..d9ebbbae01 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -6,6 +6,12 @@ on:
   schedule:
     # Runs every day at 23:00.
     - cron: "0 23 * * *"
+  workflow_dispatch:
+    inputs:
+      first_commit:
+        description: "Argument to be passed to the overnight benchmark script."
+        required: false
+        type: string
 
 jobs:
   benchmark:
@@ -64,7 +70,12 @@ jobs:
 
       - name: Run overnight benchmarks
         run: |
-          first_commit=$(git log --after="$(date -d "1 day ago" +"%Y-%m-%d") 23:00:00" --pretty=format:"%h" | tail -n 1)
+          first_commit=${{ inputs.first_commit }}
+          if [ "$first_commit" != "" ]
+          then
+            first_commit=$(git log --after="$(date -d "1 day ago" +"%Y-%m-%d") 23:00:00" --pretty=format:"%h" | tail -n 1)
+          fi
+          
           if [ "$first_commit" != "" ]
           then
             nox --session="benchmarks(overnight)" -- $first_commit
diff --git a/benchmarks/benchmarks/generate_data/__init__.py b/benchmarks/benchmarks/generate_data/__init__.py
index 78b971d9de..52a5aceca8 100644
--- a/benchmarks/benchmarks/generate_data/__init__.py
+++ b/benchmarks/benchmarks/generate_data/__init__.py
@@ -113,7 +113,7 @@ def load_realised():
     file loading, but some benchmarks are only meaningful if starting with real
     arrays.
     """
-    from iris.fileformats.netcdf import _get_cf_var_data as pre_patched
+    from iris.fileformats.netcdf.loader import _get_cf_var_data as pre_patched
 
     def patched(cf_var, filename):
         return as_concrete_data(pre_patched(cf_var, filename))