diff --git a/Kconfig.defaults b/Kconfig.defaults
index 3e98206f..c07438d6 100644
--- a/Kconfig.defaults
+++ b/Kconfig.defaults
@@ -110,6 +110,9 @@ config FILE_SYSTEM
 config FAT_FILESYSTEM_ELM
 	default y
 
+config FS_FATFS_HAS_RTC
+	default y
+
 config FS_FATFS_LFN
 	default y
 choice FS_FATFS_LFN_MODE
diff --git a/prj.conf b/prj.conf
index 6e2a1100..1a0a04c0 100644
--- a/prj.conf
+++ b/prj.conf
@@ -172,6 +172,7 @@ CONFIG_SDHC=y
 CONFIG_LOG=y
 CONFIG_FILE_SYSTEM=y
 CONFIG_FAT_FILESYSTEM_ELM=y
+CONFIG_FS_FATFS_HAS_RTC=y
 
 # Enable SDHC interface
 CONFIG_DISK_DRIVERS=y
diff --git a/prj_fota.conf b/prj_fota.conf
index 6b7263a0..0aee2b1b 100644
--- a/prj_fota.conf
+++ b/prj_fota.conf
@@ -188,6 +188,7 @@ CONFIG_SDHC=y
 CONFIG_LOG=y
 CONFIG_FILE_SYSTEM=y
 CONFIG_FAT_FILESYSTEM_ELM=y
+CONFIG_FS_FATFS_HAS_RTC=y
 
 # Enable SDHC interface
 CONFIG_DISK_DRIVERS=y
diff --git a/src/SD_Card/SD_Card_Manager/CMakeLists.txt b/src/SD_Card/SD_Card_Manager/CMakeLists.txt
index d93a7c09..ae3bf3a0 100644
--- a/src/SD_Card/SD_Card_Manager/CMakeLists.txt
+++ b/src/SD_Card/SD_Card_Manager/CMakeLists.txt
@@ -1,4 +1,5 @@
 
 target_sources(app PRIVATE
 		   ${CMAKE_CURRENT_SOURCE_DIR}/SD_Card_Manager.cpp
+		   ${CMAKE_CURRENT_SOURCE_DIR}/fatfs_time.c
 )
diff --git a/src/SD_Card/SD_Card_Manager/fatfs_time.c b/src/SD_Card/SD_Card_Manager/fatfs_time.c
new file mode 100644
index 00000000..1e862792
--- /dev/null
+++ b/src/SD_Card/SD_Card_Manager/fatfs_time.c
@@ -0,0 +1,55 @@
+#include <stdbool.h>
+#include <stdint.h>
+#include <time.h>
+#include <ff.h>
+
+#include "time_sync.h"
+
+#define FAT_YEAR_MIN 1980U
+#define FAT_YEAR_MAX 2107U
+#define UNIX_US_PER_SECOND 1000000ULL
+#define TM_YEAR_BASE 1900U /* struct tm.tm_year stores years since 1900. */
+
+/* 2022-01-01 matches FatFs/Zephyr's no-RTC fallback date and is used until phone time sync is available. */
+#define FATFS_FALLBACK_TIME \
+	(((DWORD)(2022U - FAT_YEAR_MIN) << 25) | ((DWORD)1U << 21) | ((DWORD)1U << 16))
+
+
+DWORD get_fattime(void)
+{
+
+	uint64_t now_us;
+	uint64_t now_seconds;
+
+	if (!time_sync_is_synced()) {
+		return FATFS_FALLBACK_TIME;
+	}
+
+	now_us = get_current_time_us();
+	now_seconds = now_us / UNIX_US_PER_SECOND;
+
+
+	time_t now = (time_t)now_seconds;
+	struct tm calendar;
+
+	if ((uint64_t)now != now_seconds || gmtime_r(&now, &calendar) == NULL) {
+		return FATFS_FALLBACK_TIME;
+	}
+
+	uint32_t year = (uint32_t)calendar.tm_year + TM_YEAR_BASE;
+
+	if (year < FAT_YEAR_MIN || year > FAT_YEAR_MAX) {
+		return FATFS_FALLBACK_TIME;
+	}
+
+	/*
+ 	* FAT directory entries store timestamps as packed date/time fields. 
+	* FatFs asks the application for that packed value via get_fattime().
+ 	*/
+	return (((DWORD)(year - FAT_YEAR_MIN) << 25) |
+			((DWORD)(calendar.tm_mon + 1) << 21) |
+			((DWORD)calendar.tm_mday << 16) |
+			((DWORD)calendar.tm_hour << 11) |
+			((DWORD)calendar.tm_min << 5) |
+			((DWORD)(calendar.tm_sec / 2)));
+}
diff --git a/src/time_sync/time_sync.c b/src/time_sync/time_sync.c
index f1841e4e..4d8a0c16 100644
--- a/src/time_sync/time_sync.c
+++ b/src/time_sync/time_sync.c
@@ -5,6 +5,7 @@
 #include <zephyr/devicetree.h>
 
 #include <zephyr/kernel.h>
+#include <zephyr/sys/atomic.h>
 #include <zephyr/sys/byteorder.h>
 #include <string.h>
 #include <limits.h>
@@ -40,6 +41,7 @@ struct __packed time_sync_packet {
 };
 
 int64_t time_offset_us = 0;
+static atomic_t time_synced;
 
 bool notify_rtt_enabled = false;
 
@@ -137,6 +139,7 @@ static ssize_t write_time_offset(
     int64_t delta;
     memcpy(&delta, buf, sizeof(delta));
     time_offset_us += delta;
+    atomic_set(&time_synced, 1);
     LOG_DBG("Received time offset update: %lld us, new time offset: %lld us", delta, time_offset_us);
 
     return len;
@@ -152,7 +155,11 @@ int init_time_sync(void) {
 	return 0;
 }
 
-inline uint64_t get_current_time_us() {
+bool time_sync_is_synced(void) {
+    return atomic_get(&time_synced) != 0;
+}
+
+uint64_t get_current_time_us(void) {
    uint64_t base_u = get_time_since_boot_us();
    int64_t base_s = (base_u > (uint64_t)INT64_MAX) ? INT64_MAX : (int64_t)base_u;
    int64_t now_s = base_s + time_offset_us;
@@ -167,7 +174,7 @@ inline uint64_t get_current_time_us() {
     return (uint64_t)now_s;
 }
 
-inline uint64_t get_time_since_boot_us() {
+uint64_t get_time_since_boot_us(void) {
     return k_ticks_to_us_floor64(k_uptime_ticks());
 }
 
diff --git a/src/time_sync/time_sync.h b/src/time_sync/time_sync.h
index a9ee8cd3..f4fe3ed1 100644
--- a/src/time_sync/time_sync.h
+++ b/src/time_sync/time_sync.h
@@ -4,19 +4,26 @@
 extern "C" {
 #endif
 
+#include <stdbool.h>
 #include <stdint.h>
 
 /**
  * @brief Get time since boot in microseconds.
  * @return Time since boot in microseconds.
  */
-uint64_t get_time_since_boot_us();
+uint64_t get_time_since_boot_us(void);
 
 /**
  * @brief Get the current synchronized time in microseconds (since 1. January 1970).
  * @return Current synchronized time in microseconds.
  */
-uint64_t get_current_time_us();
+uint64_t get_current_time_us(void);
+
+/**
+ * @brief Check whether the wall-clock time has been synchronized.
+ * @return True after the Time Offset characteristic has been written.
+ */
+bool time_sync_is_synced(void);
 
 /**
  * @brief Initialize the time synchronization module.
@@ -27,4 +34,4 @@ int init_time_sync();
 
 #ifdef __cplusplus
 }
-#endif
\ No newline at end of file
+#endif