Compact storage of time using bitwise operations

ampm.c

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

typedef short unsigned int tt;
typedef unsigned char byte;

tt TimeToTT(char *time_string) { /* example input: "12:24AM" */
    char *hour_string = strtok(time_string, ":"); byte hours = atoi(hour_string);
    char *min_string = strtok(NULL, ":"); byte minutes = atoi(min_string);

    bool is_pm = strstr(&min_string[strlen(min_string) - 2 - 1], "PM");

    tt res = 0;
    res |= is_pm;          /* 1 bit */
    res |= (minutes << 1); /* 6bits */
    res |= (hours << 6);   /* 4bits */

    return res;
}

char* TTtoTime(tt a) {
    char* res = malloc(7 * sizeof(char));

    res[0] = '\0';

    unsigned short hours = (a >> 6); /* 4 most left bits */
    unsigned short minutes = (a >> 1) & 0x1F; /* 6 most right bits */
    bool is_pm = a & 0x01; /* 1 most right bit */

    char* hrs_str = malloc(sizeof(char) * 3); sprintf(hrs_str, "%u", hours);
    strcat(res, hrs_str);

    strcat(res, ":");

    char* min_str = malloc(sizeof(char) * 3); sprintf(min_str, "%u", minutes);
    strcat(res, min_str);

    strcat(res, (is_pm ? "PM" : "AM"));

    return res;
}

int main(void) {
    char time[] = "3:24PM";
    tt res = TimeToTT(time);
    printf("TT value: %d\n", res); /* 241 */

    char* time_reconstructed = TTtoTime(res);
    printf("Reconstructed time: %s", time_reconstructed); /* 3:24PM */

    return 0;
}