Scalability of running commands from user input

Here is some code I have that has been extracted and shrunk down from a project of mine.

#include <stdio.h>
#include <stdint.h>
#include <time.h>
#include <string.h>

#define streq(x, y) (strcmp((x), (y)) == 0)
#define ARRAY_SIZE(x) (sizeof(x)/sizeof(x[0]))

typedef struct
{
    const char *cmd;
    void* (*fn)(void);
} __attribute__((__packed__)) Command;

void* getTime(void)
{
    return ((void*)((uintptr_t)time(NULL)));
}

void* getDay(void)
{
    time_t t = time(NULL);
    struct tm tm = *localtime(&t);
    return ((void*)((uintptr_t)(tm.tm_wday)));
}

static Command commands[] =
{
    {"time", getTime},
    {"day", getDay},
};

int main(int argc, char *argv[])
{
    for (int i = 0; i < ARRAY_SIZE(commands); ++i)
    {
        Command *p = commands+i;
        if (streq(argv[1], p->cmd)) printf("%d\n", (int)p->fn());
    }
}

When run with some given input, it runs the method associated with that input. Since this is a scaled down version of my project, it can only run two commands.

$ ./test-command day
4

Right now, my implementation should run with \$ O \left( n\right)\$ time complexity. This would be unacceptable with the hundreds of thousands of commands my project could scale to. I am looking for reviews on scalability and optimization.