diff --git a/esphome/components/time/posix_tz.cpp b/esphome/components/time/posix_tz.cpp
index d54e611443..ab1d07811b 100644
--- a/esphome/components/time/posix_tz.cpp
+++ b/esphome/components/time/posix_tz.cpp
@@ -342,7 +342,7 @@ bool __attribute__((noinline)) is_in_dst(time_t utc_epoch, const ParsedTimezone
   }
 }
 
-size_t format_dst_rule(const DSTRule &rule, std::span<char, 24> buf) {
+size_t format_dst_rule(const DSTRule &rule, std::span<char, DST_RULE_BUF_SIZE> buf) {
   // Format rule part
   int pos = 0;
   switch (rule.type) {
diff --git a/esphome/components/time/posix_tz.h b/esphome/components/time/posix_tz.h
index fa2e7f8ab6..e994d53fda 100644
--- a/esphome/components/time/posix_tz.h
+++ b/esphome/components/time/posix_tz.h
@@ -113,11 +113,14 @@ time_t calculate_dst_transition(int year, const DSTRule &rule, int32_t base_offs
 /// @return true if DST is in effect at the given time
 bool is_in_dst(time_t utc_epoch, const ParsedTimezone &tz);
 
+/// Buffer size for format_dst_rule output
+static constexpr size_t DST_RULE_BUF_SIZE = 24;
+
 /// Format a DST rule for logging/display
 /// @param rule The DST rule to format
-/// @param buf Output buffer (24 bytes recommended)
+/// @param buf Output buffer
 /// @return Number of characters written (excluding null terminator)
-size_t format_dst_rule(const DSTRule &rule, std::span<char, 24> buf);
+size_t format_dst_rule(const DSTRule &rule, std::span<char, DST_RULE_BUF_SIZE> buf);
 
 }  // namespace internal
 
diff --git a/esphome/components/time/real_time_clock.cpp b/esphome/components/time/real_time_clock.cpp
index 649cacd3f0..025d613a0d 100644
--- a/esphome/components/time/real_time_clock.cpp
+++ b/esphome/components/time/real_time_clock.cpp
@@ -30,7 +30,7 @@ void RealTimeClock::dump_config() {
   ESP_LOGCONFIG(TAG, "Timezone: UTC%+d:%02d", std_hours, std_mins);
   if (this->parsed_tz_.has_dst) {
     int dst_hours = -this->parsed_tz_.dst_offset_seconds / 3600;
-    char start_buf[24], end_buf[24];
+    char start_buf[internal::DST_RULE_BUF_SIZE], end_buf[internal::DST_RULE_BUF_SIZE];
     internal::format_dst_rule(this->parsed_tz_.dst_start, start_buf);
     internal::format_dst_rule(this->parsed_tz_.dst_end, end_buf);
     ESP_LOGCONFIG(TAG, "  DST: UTC%+d, %s - %s", dst_hours, start_buf, end_buf);
diff --git a/tests/components/time/posix_tz_parser.cpp b/tests/components/time/posix_tz_parser.cpp
index fb3af1ae35..5311edbf27 100644
--- a/tests/components/time/posix_tz_parser.cpp
+++ b/tests/components/time/posix_tz_parser.cpp
@@ -843,7 +843,7 @@ TEST(PosixTzParser, FormatDstRuleMonthWeekDay) {
   rule.day_of_week = 0;
   rule.time_seconds = 2 * 3600;  // 2:00
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "M3.2.0/2");
   EXPECT_EQ(len, 8u);
@@ -855,7 +855,7 @@ TEST(PosixTzParser, FormatDstRuleJulian) {
   rule.day = 60;
   rule.time_seconds = 2 * 3600;
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "J60/2");
   EXPECT_EQ(len, 5u);
@@ -867,7 +867,7 @@ TEST(PosixTzParser, FormatDstRuleDayOfYear) {
   rule.day = 300;
   rule.time_seconds = 2 * 3600;
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "300/2");
   EXPECT_EQ(len, 5u);
@@ -881,7 +881,7 @@ TEST(PosixTzParser, FormatDstRuleWithMinutes) {
   rule.day_of_week = 0;
   rule.time_seconds = 2 * 3600 + 30 * 60;  // 2:30
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "M11.1.0/2:30");
   EXPECT_EQ(len, 12u);
@@ -895,7 +895,7 @@ TEST(PosixTzParser, FormatDstRuleWithSeconds) {
   rule.day_of_week = 0;
   rule.time_seconds = 2 * 3600 + 30 * 60 + 45;  // 2:30:45
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "M3.5.0/2:30:45");
   EXPECT_EQ(len, 14u);
@@ -909,7 +909,7 @@ TEST(PosixTzParser, FormatDstRuleNegativeTime) {
   rule.day_of_week = 0;
   rule.time_seconds = -1 * 3600;  // -1:00 (11 PM previous day)
 
-  char buf[24];
+  char buf[internal::DST_RULE_BUF_SIZE];
   size_t len = internal::format_dst_rule(rule, buf);
   EXPECT_STREQ(buf, "M3.2.0-1");
   EXPECT_EQ(len, 8u);