From a91a5766545a1f813cb849c551fdb8e61816df38 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 18 Jun 2026 16:27:15 -0500
Subject: [PATCH] merge

---
 esphome/components/time/real_time_clock.cpp | 31 +++++++++++++++++++++
 esphome/components/time/real_time_clock.h   | 28 +++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/esphome/components/time/real_time_clock.cpp b/esphome/components/time/real_time_clock.cpp
index 894e7aed52..4e623942ac 100644
--- a/esphome/components/time/real_time_clock.cpp
+++ b/esphome/components/time/real_time_clock.cpp
@@ -107,4 +107,35 @@ void RealTimeClock::synchronize_epoch_(uint32_t epoch) {
   this->time_sync_callback_.call();
 }
 
+#ifdef USE_TIME_TIMEZONE
+void RealTimeClock::apply_timezone_(const char *tz) {
+  ParsedTimezone parsed{};
+
+  // Handle null or empty input - use UTC
+  if (tz == nullptr || *tz == '\0') {
+    // Skip if already UTC
+    if (!get_global_tz().has_dst() && get_global_tz().std_offset_seconds == 0) {
+      return;
+    }
+    set_global_tz(parsed);
+    return;
+  }
+
+#ifdef USE_HOST
+  // On host platform, also set TZ environment variable for libc compatibility
+  setenv("TZ", tz, 1);
+  tzset();
+#endif
+
+  // Parse the POSIX TZ string using our custom parser
+  if (!parse_posix_tz(tz, parsed)) {
+    ESP_LOGW(TAG, "Failed to parse timezone: %s", tz);
+    return;
+  }
+
+  // Set global timezone for all time conversions
+  set_global_tz(parsed);
+}
+#endif
+
 }  // namespace esphome::time
diff --git a/esphome/components/time/real_time_clock.h b/esphome/components/time/real_time_clock.h
index 931cd1e946..06ee2ea5af 100644
--- a/esphome/components/time/real_time_clock.h
+++ b/esphome/components/time/real_time_clock.h
@@ -22,6 +22,30 @@ class RealTimeClock : public PollingComponent {
  public:
   explicit RealTimeClock();
 
+#ifdef USE_TIME_TIMEZONE
+  /// Set the time zone from a POSIX TZ string.
+  void set_timezone(const char *tz) { this->apply_timezone_(tz); }
+
+  /// Set the time zone from a character buffer with known length.
+  /// The buffer does not need to be null-terminated.
+  void set_timezone(const char *tz, size_t len) {
+    if (tz == nullptr) {
+      this->apply_timezone_(nullptr);
+      return;
+    }
+    // Stack buffer - TZ strings from tzdata are typically short (< 50 chars)
+    char buf[128];
+    if (len >= sizeof(buf))
+      len = sizeof(buf) - 1;
+    memcpy(buf, tz, len);
+    buf[len] = '\0';
+    this->apply_timezone_(buf);
+  }
+
+  /// Set the time zone from a std::string.
+  void set_timezone(const std::string &tz) { this->apply_timezone_(tz.c_str()); }
+#endif
+
   /// Get the time in the currently defined timezone.
   ESPTime now();
 
@@ -41,6 +65,10 @@ class RealTimeClock : public PollingComponent {
   /// Report a unix epoch as current time.
   void synchronize_epoch_(uint32_t epoch);
 
+#ifdef USE_TIME_TIMEZONE
+  void apply_timezone_(const char *tz);
+#endif
+
   LazyCallbackManager<void()> time_sync_callback_;
 };