Half Day Linux Kernel Module, shows usage of timers in kernel fairly well but otherwise useless

robbbmod_sept_7.c

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/time.h>
#include <linux/timer.h>

#define TEN_SECS_IN_MS 10000
#define WORK_BEFORE 1473336000
#define WORK_AFTER 1473350400

static int robbb_mod_workflag = 0;
static struct timer_list robbb_mod_timer;

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Robb Manes");
MODULE_DESCRIPTION("Robb is taking a half day.");
MODULE_VERSION("0.1");

static int __init half_day_init(void);
void robbb_timer_callback(unsigned long data);
static void __exit half_day_exit(void);

static int __init half_day_init(void)
{
	int ret = 0;

	printk("Registering Robb's half day module...\n");

	setup_timer(&robbb_mod_timer, robbb_timer_callback, 0);

	ret = mod_timer(&robbb_mod_timer, jiffies + msecs_to_jiffies(10));
	if(ret)
		printk("Unable to load timer robbb_mod_timer!\n");

	return 0;
}

void robbb_timer_callback(unsigned long data)
{
	struct timeval tv;

	do_gettimeofday(&tv);

	/* Todo - convert and print local times based on epoch in &tv */
	if((WORK_BEFORE >= tv.tv_sec))
	{
		printk("Robb is currently not working yet!\n");
	}
	else if((WORK_BEFORE <= tv.tv_sec) && (WORK_AFTER >= tv.tv_sec))
	{
		 printk("Robb is currently at work!\n");
	}
	else if(WORK_AFTER <= tv.tv_sec)
	{
		printk("Robb has left work, and taken his half day!\n");
		robbb_mod_workflag = 1;
	}

	if(!robbb_mod_workflag)
		mod_timer(&robbb_mod_timer, jiffies + msecs_to_jiffies(TEN_SECS_IN_MS));
}

static void __exit half_day_exit(void)
{
	printk("Unloading robbb's half-day module...\n");

	if(del_timer(&robbb_mod_timer))
		printk("Timer still in use, unable to delete robbb_mod_timer.\n");

	return;
}

module_init(half_day_init);
module_exit(half_day_exit);

Makefile

obj-m += robbbmod_sept_7.o

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean