diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15f1f5b2..7631294a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,10 @@ adheres to [Semantic Versioning](https://semver.org/).
 
 ### Fixed
 
+- Model time budgets now stop at their deadline, including a zero-second
+  budget when the clock has not advanced. This prevents optional model calls
+  from starting after the time allowance has been consumed.
+
 - The Polars engine no longer silently loses rows from a zero-column pandas
   input. It uses the recorded pandas fallback, preserving the input index and
   row counts with pandas output; `fallback_policy="error"` rejects the run
diff --git a/docs/semantic-models.md b/docs/semantic-models.md
index 9f6ca9ea..18f32609 100644
--- a/docs/semantic-models.md
+++ b/docs/semantic-models.md
@@ -174,6 +174,10 @@ An exhausted budget stops the embedding backend cleanly (proposals already
 made stand; nothing is partially applied) and records a report fallback
 event. Deterministic and memory backends are never metered.
 
+The time budget expires when elapsed time reaches `max_seconds`. A value of
+`0` refuses model work immediately, even when the clock has not advanced since
+the budget was created. Leaving `max_seconds` unset imposes no time ceiling.
+
 ## Graceful degradation
 
 Requesting `"embedding"` without the extra or the model **never crashes**:
diff --git a/src/freshdata/semantic/backends/base.py b/src/freshdata/semantic/backends/base.py
index 892a28da..75812df1 100644
--- a/src/freshdata/semantic/backends/base.py
+++ b/src/freshdata/semantic/backends/base.py
@@ -68,7 +68,7 @@ def _check_time(self) -> None:
         if (
             not self.exhausted_reason
             and self.max_seconds is not None
-            and time.monotonic() - self.started_at > self.max_seconds
+            and time.monotonic() - self.started_at >= self.max_seconds
         ):
             self.exhausted_reason = f"max_seconds={self.max_seconds} exceeded"
 
diff --git a/tests/test_semantic_backends.py b/tests/test_semantic_backends.py
index a6c084d2..d8a51ce5 100644
--- a/tests/test_semantic_backends.py
+++ b/tests/test_semantic_backends.py
@@ -3,6 +3,8 @@
 
 from __future__ import annotations
 
+import time
+
 import numpy as np
 import pandas as pd
 import pytest
@@ -357,6 +359,38 @@ def test_budget_from_config_parses_fields():
     assert Budget.from_config({"max_columns": -1}).max_columns is None
 
 
+@pytest.mark.parametrize("max_seconds", [0.0, 0.5])
+def test_time_budget_refuses_work_at_its_deadline(monkeypatch, max_seconds):
+    budget = Budget(max_seconds=max_seconds, started_at=100.0)
+    monkeypatch.setattr(time, "monotonic", lambda: 100.0 + max_seconds)
+
+    assert not budget.try_column(3)
+    assert not budget.try_model_call()
+    assert budget.columns_used == budget.distinct_values_used == budget.model_calls_used == 0
+    assert "max_seconds" in budget.exhausted_reason
+
+
+def test_time_budget_reservations_stop_at_the_deadline(monkeypatch):
+    now = [100.499]
+    monkeypatch.setattr(time, "monotonic", lambda: now[0])
+    budget = Budget(max_seconds=0.5, started_at=100.0)
+    assert budget.try_column(3)
+    assert budget.try_model_call()
+
+    now[0] = 100.5
+    assert not budget.try_column(2)
+    assert not budget.try_model_call()
+    assert (budget.columns_used, budget.distinct_values_used, budget.model_calls_used) == (1, 3, 1)
+
+
+def test_unset_time_budget_remains_unbounded(monkeypatch):
+    monkeypatch.setattr(time, "monotonic", lambda: 10000.0)
+    budget = Budget(started_at=100.0)
+    assert budget.try_column(3)
+    assert budget.try_model_call()
+    assert not budget.exhausted
+
+
 @pytest.mark.parametrize(
     "budget_dict, expected_reason",
     [
@@ -367,12 +401,13 @@ def test_budget_from_config_parses_fields():
     ],
 )
 def test_budget_exhaustion_stops_cleanly(encoder_factory, budget_dict, expected_reason):
-    encoder_factory(_status_vectors())
+    encoder = encoder_factory(_status_vectors())
     df = _status_frame()
     out, report = fd.clean(
         df, config=_status_config(semantic_budget=budget_dict), return_report=True
     )
     assert not [a for a in report.actions if a.model_id.endswith(":embedding")]
+    assert encoder.calls == []
     events = [e for e in report.fallback_events if e["backend"] == "embedding"]
     assert events and expected_reason in events[0]["fallback_reason"]
     # Deterministic experts still ran despite the exhausted model budget.