diff --git a/docs/hackerrank/warmup/time_conversion.md b/docs/hackerrank/warmup/time_conversion.md
new file mode 100644
index 0000000..273cd14
--- /dev/null
+++ b/docs/hackerrank/warmup/time_conversion.md
@@ -0,0 +1,53 @@
+# [Time Conversion](https://www.hackerrank.com/challenges/time-conversion)
+
+Difficulty: #easy
+Category: #warmup
+
+Given a time in
+12-[hour AM/PM format](https://en.wikipedia.org/wiki/12-hour_clock),
+convert it to military (24-hour) time.
+
+Note:
+
+- 12:00:00AM on a 12-hour clock is 00:00:00 on a 24-hour clock.
+- 12:00:00PM on a 12-hour clock is 12:00:00 on a 24-hour clock.
+
+## Example
+
+- s = '12:01:00PM' \
+  Return '12:01:00'
+- s = '12:01:00AM' \
+  Return '00:01:00'
+
+## Function Description
+
+Complete the timeConversion function in the editor below.
+It should return a new string representing the input time in 24 hour format
+timeConversion has the following parameter(s):
+
+- string s: a time in 12 hour format
+
+## Returns
+
+- string: the time in 24 hour format
+
+## Input Format
+
+A single string s that represents a time in 12-hour clock format
+(i.e.: hh_mm_ssAM or hh:mm:ssPM).
+
+## Constraints
+
+- All input times are valid
+
+## Sample Input 0
+
+```text
+07:05:45PM
+```
+
+## Sample Output 0
+
+```text
+19:05:45
+```
diff --git a/src/lib/exercises/include/exercises/hackerrank/warmup/time_conversion.h b/src/lib/exercises/include/exercises/hackerrank/warmup/time_conversion.h
new file mode 100644
index 0000000..20809c7
--- /dev/null
+++ b/src/lib/exercises/include/exercises/hackerrank/warmup/time_conversion.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+char *HACKERRANK_WARMUP_getStringFragment(const char *s, unsigned long len,
+                                          unsigned long from, unsigned long to);
+
+char *HACKERRANK_WARMUP_timeConversion(const char *s);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
diff --git a/src/lib/exercises/src/hackerrank/warmup/time_conversion.c b/src/lib/exercises/src/hackerrank/warmup/time_conversion.c
new file mode 100644
index 0000000..95dcd3f
--- /dev/null
+++ b/src/lib/exercises/src/hackerrank/warmup/time_conversion.c
@@ -0,0 +1,68 @@
+#include <exercises/hackerrank/warmup/time_conversion.h>
+
+/**
+ * @link Problem definition [[docs/hackerrank/warmup/time_conversion.md]]
+ */
+
+#include <stdio.h>  // snprintf
+#include <stdlib.h> // malloc, free, strtol
+#include <string.h> // strcmp, strnlen
+
+#define HACKERRANK_WARMUP_LONG_TIME_FORMAT_SIZE 10
+#define HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE 8
+#define HACKERRANK_WARMUP_HOUR_FORMAT_SIZE 2
+
+char *HACKERRANK_WARMUP_timeConversion(const char *s) {
+  if (s == NULL) {
+    return NULL;
+  }
+
+  size_t s_len = strnlen(s, HACKERRANK_WARMUP_LONG_TIME_FORMAT_SIZE);
+
+  if (s_len != HACKERRANK_WARMUP_LONG_TIME_FORMAT_SIZE) {
+    return NULL;
+  }
+
+  char hour_str[HACKERRANK_WARMUP_HOUR_FORMAT_SIZE + 1];
+
+  hour_str[0] = s[0];
+  hour_str[1] = s[1];
+  hour_str[2] = '\0';
+
+  char meridian[3];
+  meridian[0] = s[s_len - 2];
+  meridian[1] = s[s_len - 1];
+  meridian[2] = '\0';
+
+  char *endptr;
+  long hour = strtol(hour_str, &endptr, 10);
+
+  if (*endptr != '\0') {
+    printf("Conversion error, non-convertible part: %s\n", endptr);
+
+    return NULL;
+  } else {
+    printf("The integer value is: %ld\n", hour);
+  }
+
+  hour = hour % 12;
+
+  if (strcmp(meridian, "PM") == 0) {
+    hour += 12;
+  }
+
+  char *conversion =
+      malloc((HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE + 1) * sizeof(char));
+
+  for (int i = 0; i < HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE; i++) {
+    conversion[i] = s[i];
+  }
+  conversion[HACKERRANK_WARMUP_SHORT_TIME_FORMAT_SIZE] = '\0';
+
+  snprintf(hour_str, HACKERRANK_WARMUP_HOUR_FORMAT_SIZE + 1, "%02ld", hour);
+
+  conversion[0] = hour_str[0];
+  conversion[1] = hour_str[1];
+
+  return conversion;
+}
diff --git a/src/tests/unit/lib/hackerrank/warmup/time_conversion.test.cpp b/src/tests/unit/lib/hackerrank/warmup/time_conversion.test.cpp
new file mode 100644
index 0000000..ac61f23
--- /dev/null
+++ b/src/tests/unit/lib/hackerrank/warmup/time_conversion.test.cpp
@@ -0,0 +1,41 @@
+#include <catch2/catch_test_macros.hpp>
+
+#include <exercises/hackerrank/warmup/time_conversion.h>
+#include <filesystem>
+#include <fstream>
+#include <nlohmann/json.hpp>
+#include <vector>
+
+using json = nlohmann::json;
+
+TEST_CASE("time_conversion JSON Test Cases",
+          "[hackerrank] [jsontestcase] [warmup]") {
+  std::filesystem::path cwd = std::filesystem::current_path();
+  std::string path =
+      cwd.string() +
+      "/unit/lib/hackerrank/warmup/time_conversion.testcases.json";
+
+  INFO("time_conversion JSON test cases FILE: " << path);
+
+  std::ifstream f(path);
+  json data = json::parse(f);
+
+  for (auto testcase : data) {
+    char *result = HACKERRANK_WARMUP_timeConversion(
+        testcase["input"].get<std::string>().c_str());
+
+    std::string result_as_string(result);
+
+    free(result);
+
+    CHECK(result_as_string == testcase["expected"]);
+  }
+}
+
+TEST_CASE("time_conversion edge cases", "[hackerrank] [helper] [warmup]") {
+  CHECK(HACKERRANK_WARMUP_timeConversion(nullptr) == nullptr);
+
+  CHECK(HACKERRANK_WARMUP_timeConversion("") == nullptr);
+
+  CHECK(HACKERRANK_WARMUP_timeConversion("aa:bb:ccXM") == nullptr);
+}
diff --git a/src/tests/unit/lib/hackerrank/warmup/time_conversion.testcases.json b/src/tests/unit/lib/hackerrank/warmup/time_conversion.testcases.json
new file mode 100644
index 0000000..16c374f
--- /dev/null
+++ b/src/tests/unit/lib/hackerrank/warmup/time_conversion.testcases.json
@@ -0,0 +1,4 @@
+[
+  { "input": "12:01:00PM", "expected": "12:01:00" },
+  { "input": "12:01:00AM", "expected": "00:01:00" }
+]