Code

#include <pebble.h>


static Window *s_main_window;

static BitmapLayer *s_background_layer;
static GBitmap *s_background_bitmap;
static int hour;


static void update_time() {

 // Get a tm structure
  time_t temp = time(NULL);
  struct tm *tick_time = localtime(&temp);

  // Create a long-lived buffer
  static char buffer[] = "00:00";

  // Write the current hours and minutes into the buffer
  if(clock_is_24h_style() == true) {
    //Use 2h hour format
    strftime(buffer, sizeof("00:00"), "%H:%M", tick_time);
  } else {
    //Use 12 hour format
    strftime(buffer, sizeof("00:00"), "%I:%M", tick_time);

hour = &ticktime.tm_hour;

}

static void main_window_load(Window *window) {

  //Create GBitmap, then set to created BitmapLayer


switch(hour){

case 00:
s_background_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_12);
break;

case 01:
s_background_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_12);
break;

case 02:
s_background_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_12);
break;

case 03:
s_background_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_12);
break;

default:
break;
}
  s_background_layer = bitmap_layer_create(GRect(0, 0, 144, 168));
  bitmap_layer_set_bitmap(s_background_layer, s_background_bitmap);
  layer_add_child(window_get_root_layer(window), bitmap_layer_get_layer(s_background_layer));



}

static void main_window_unload(Window *window) {

  //Destroy GBitmap
  gbitmap_destroy(s_background_bitmap);

  //Destroy BitmapLayer
  bitmap_layer_destroy(s_background_layer);

 // Make sure the time is displayed from the start
  update_time();
}

static void init() {
  // Create main Window element and assign to pointer
  s_main_window = window_create();

  // Set handlers to manage the elements inside the Window
  window_set_window_handlers(s_main_window, (WindowHandlers) {
    .load = main_window_load,
    .unload = main_window_unload
  });

  // Show the Window on the watch, with animated=true
  window_stack_push(s_main_window, true);

}

static void deinit() {
  // Destroy Window
  window_destroy(s_main_window);
}

int main(void) {
  init();
  app_event_loop();
  deinit();
}