diff --git a/tests/functional/alfven_wave/alfven_wave1d.py b/tests/functional/alfven_wave/alfven_wave1d.py
index 50c49350b..ef6a822f9 100644
--- a/tests/functional/alfven_wave/alfven_wave1d.py
+++ b/tests/functional/alfven_wave/alfven_wave1d.py
@@ -91,7 +91,7 @@ def vthz(x):
 
     ph.ElectronModel(closure="isothermal", Te=0.0)
 
-    timestamps = [0, int(final_time / 2), final_time]
+    timestamps = np.arange(0, sim.final_time, sim.final_time / 10)
 
     for quantity in ["E", "B"]:
         ph.ElectromagDiagnostics(quantity=quantity, write_timestamps=timestamps)
diff --git a/tests/functional/dispersion/dispersion.py b/tests/functional/dispersion/dispersion.py
index 63bfd16a3..ad6619984 100644
--- a/tests/functional/dispersion/dispersion.py
+++ b/tests/functional/dispersion/dispersion.py
@@ -167,10 +167,14 @@ def vthz(x):
     timestamps = np.arange(0, sim.final_time + sim.time_step, sim.time_step)
 
     for quantity in ["E", "B"]:
-        ph.ElectromagDiagnostics(quantity=quantity, write_timestamps=timestamps)
+        ph.ElectromagDiagnostics(
+            quantity=quantity, write_timestamps=timestamps, flush_every=0
+        )
 
     for quantity in ["density", "bulkVelocity"]:
-        ph.FluidDiagnostics(quantity=quantity, write_timestamps=timestamps)
+        ph.FluidDiagnostics(
+            quantity=quantity, write_timestamps=timestamps, flush_every=0
+        )
 
     return sim