diff --git a/el-compiler/runtime/el_runtime.c b/el-compiler/runtime/el_runtime.c
index 4ac9eae..4c5a2d3 100644
--- a/el-compiler/runtime/el_runtime.c
+++ b/el-compiler/runtime/el_runtime.c
@@ -3889,8 +3889,8 @@ el_val_t str_pad_right(el_val_t s, el_val_t width, el_val_t pad) {
     return str_pad(EL_CSTR(s), (int64_t)width, EL_CSTR(pad), 0);
 }
 
-el_val_t str_format(el_val_t template, el_val_t data) {
-    const char* tpl = EL_CSTR(template);
+el_val_t str_format(el_val_t fmt, el_val_t data) {
+    const char* tpl = EL_CSTR(fmt);
     if (!tpl) return el_wrap_str(el_strdup(""));
     JsonBuf b; jb_init(&b);
     const char* p = tpl;
diff --git a/el-compiler/runtime/el_runtime.h b/el-compiler/runtime/el_runtime.h
index 9e9846c..6939d01 100644
--- a/el-compiler/runtime/el_runtime.h
+++ b/el-compiler/runtime/el_runtime.h
@@ -259,6 +259,63 @@ el_val_t  time_from_parts(el_val_t secs, el_val_t ns, el_val_t tz);
 el_val_t  time_add(el_val_t ts, el_val_t n, el_val_t unit);
 el_val_t  time_diff(el_val_t ts1, el_val_t ts2, el_val_t unit);
 
+/* ── Instant + Duration: first-class temporal types ──────────────────────────
+ * Both types share the el_val_t (int64) slot. Instants are nanoseconds
+ * since the Unix epoch; Durations are signed nanoseconds. Type discipline
+ * is enforced at codegen-time: BinOps on names registered as Instant or
+ * Duration route through the typed wrappers below; mismatches like
+ * Instant+Instant become #error at the C compiler.
+ *
+ * Postfix literals — `30.seconds`, `1.hour`, `500.millis`, `30.nanos` — are
+ * recognised by the parser as DurationLit AST nodes and lowered to literal
+ * int64 nanoseconds at codegen time. The runtime never sees the units. */
+
+el_val_t  el_now_instant(void);
+el_val_t  now(void);
+el_val_t  unix_seconds(el_val_t n);
+el_val_t  unix_millis(el_val_t n);
+el_val_t  instant_from_iso8601(el_val_t s);
+
+el_val_t  el_duration_from_nanos(el_val_t ns);
+el_val_t  duration_seconds(el_val_t n);
+el_val_t  duration_millis(el_val_t n);
+el_val_t  duration_nanos(el_val_t n);
+
+el_val_t  el_instant_add_dur(el_val_t inst, el_val_t dur);
+el_val_t  el_instant_sub_dur(el_val_t inst, el_val_t dur);
+el_val_t  el_instant_diff(el_val_t a, el_val_t b);
+el_val_t  el_duration_add(el_val_t a, el_val_t b);
+el_val_t  el_duration_sub(el_val_t a, el_val_t b);
+el_val_t  el_duration_scale(el_val_t dur, el_val_t scalar);
+el_val_t  el_duration_div(el_val_t dur, el_val_t scalar);
+
+el_val_t  el_instant_lt(el_val_t a, el_val_t b);
+el_val_t  el_instant_le(el_val_t a, el_val_t b);
+el_val_t  el_instant_gt(el_val_t a, el_val_t b);
+el_val_t  el_instant_ge(el_val_t a, el_val_t b);
+el_val_t  el_instant_eq(el_val_t a, el_val_t b);
+el_val_t  el_instant_ne(el_val_t a, el_val_t b);
+el_val_t  el_duration_lt(el_val_t a, el_val_t b);
+el_val_t  el_duration_le(el_val_t a, el_val_t b);
+el_val_t  el_duration_gt(el_val_t a, el_val_t b);
+el_val_t  el_duration_ge(el_val_t a, el_val_t b);
+el_val_t  el_duration_eq(el_val_t a, el_val_t b);
+el_val_t  el_duration_ne(el_val_t a, el_val_t b);
+
+el_val_t  instant_to_unix_seconds(el_val_t i);
+el_val_t  instant_to_unix_millis(el_val_t i);
+el_val_t  instant_to_iso8601(el_val_t i);
+el_val_t  duration_to_seconds(el_val_t d);
+el_val_t  duration_to_millis(el_val_t d);
+el_val_t  duration_to_nanos(el_val_t d);
+
+el_val_t  el_sleep_duration(el_val_t dur);
+el_val_t  unix_timestamp(void);
+
+el_val_t  ttl_cache_set(el_val_t key, el_val_t value);
+el_val_t  ttl_cache_get(el_val_t key, el_val_t max_age);
+el_val_t  ttl_cache_age(el_val_t key);
+
 /* ── UUID ────────────────────────────────────────────────────────────────── */
 
 el_val_t  uuid_new(void);
@@ -301,7 +358,7 @@ el_val_t  str_char_at(el_val_t s, el_val_t i);
 el_val_t  str_char_code(el_val_t s, el_val_t i);
 el_val_t  str_pad_left(el_val_t s, el_val_t width, el_val_t pad);
 el_val_t  str_pad_right(el_val_t s, el_val_t width, el_val_t pad);
-el_val_t  str_format(el_val_t template, el_val_t data);
+el_val_t  str_format(el_val_t fmt, el_val_t data);
 el_val_t  str_lower(el_val_t s);
 el_val_t  str_upper(el_val_t s);