diff --git a/.github/workflows/ci-test.yml b/.github/workflows/ci-test.yml
index f7f1fe672a8..2f4e91d642f 100644
--- a/.github/workflows/ci-test.yml
+++ b/.github/workflows/ci-test.yml
@@ -108,37 +108,6 @@ jobs:
       run: sudo -E ctest --output-on-failure --schedule-random
       working-directory: ./build
 
-  # Build with gcc and test p4c on Ubuntu 18.04.
-  test-ubuntu18:
-    strategy:
-      fail-fast: false
-    runs-on: ubuntu-latest
-    env:
-      CTEST_PARALLEL_LEVEL: 4
-    steps:
-    - uses: actions/checkout@v3
-      with:
-        submodules: recursive
-        fetch-depth: 0
-
-    - name: ccache
-      uses: hendrikmuhs/ccache-action@v1
-      with:
-        key: test-ubuntu-18.04-gcc
-        max-size: 1000M
-
-    - name: Build (Ubuntu 18.04, GCC)
-      run: |
-        docker build -t p4c --build-arg BASE_IMAGE=ubuntu:18.04 --build-arg IMAGE_TYPE=test \
-        --build-arg ENABLE_TEST_TOOLS=OFF .
-        ./tools/export_ccache.sh
-
-      # run with sudo (...) --privileged
-      # this is needed to create network namespaces for the ebpf tests.
-    - name: Run tests (Ubuntu 18.04)
-      run: |
-        sudo -E docker run --privileged -w /p4c/build -e $CTEST_PARALLEL_LEVEL p4c ctest --output-on-failure --schedule-random
-
   # Build and test p4c on Fedora.
   test-fedora-linux:
     strategy:
diff --git a/.github/workflows/ci-ubuntu-18-nightly.yml b/.github/workflows/ci-ubuntu-18-nightly.yml
new file mode 100644
index 00000000000..feab1558ada
--- /dev/null
+++ b/.github/workflows/ci-ubuntu-18-nightly.yml
@@ -0,0 +1,43 @@
+name: "test-p4c-ubuntu-18.04"
+
+on:
+  schedule:
+    # Every day on midnight UTC
+    - cron: '0 0 * * *'
+
+# Cancel any preceding run on the pull request.
+concurrency:
+  group: test-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
+
+jobs:
+  # Build with gcc and test p4c on Ubuntu 18.04.
+  test-ubuntu18:
+    strategy:
+      fail-fast: false
+    runs-on: ubuntu-latest
+    env:
+      CTEST_PARALLEL_LEVEL: 4
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        submodules: recursive
+        fetch-depth: 0
+
+    - name: ccache
+      uses: hendrikmuhs/ccache-action@v1
+      with:
+        key: test-ubuntu-18.04-gcc
+        max-size: 1000M
+
+    - name: Build (Ubuntu 18.04, GCC)
+      run: |
+        docker build -t p4c --build-arg BASE_IMAGE=ubuntu:18.04 --build-arg IMAGE_TYPE=test \
+        --build-arg ENABLE_TEST_TOOLS=OFF .
+        ./tools/export_ccache.sh
+
+      # run with sudo (...) --privileged
+      # this is needed to create network namespaces for the ebpf tests.
+    - name: Run tests (Ubuntu 18.04)
+      run: |
+        sudo -E docker run --privileged -w /p4c/build -e $CTEST_PARALLEL_LEVEL p4c ctest --output-on-failure --schedule-random
diff --git a/.github/workflows/ci-validation.yml b/.github/workflows/ci-validation-nightly.yml
similarity index 93%
rename from .github/workflows/ci-validation.yml
rename to .github/workflows/ci-validation-nightly.yml
index dee4e98d0a0..ed5f308a4a8 100644
--- a/.github/workflows/ci-validation.yml
+++ b/.github/workflows/ci-validation-nightly.yml
@@ -1,10 +1,9 @@
 name: "validate-p4c"
 
 on:
-  push:
-    branches: [ main ]
-  pull_request:
-    branches: [ main ]
+  schedule:
+    # Every day on midnight UTC
+    - cron: '0 0 * * *'
 
 # Cancel any preceding run on the pull request.
 concurrency: