static unsigned char xdata str_buffer[20]; //not sure if static reqd, its in main()
...
strcpy(str_buffer,dec2ascii(read_hour())); //read_hour() returns 12 in dec (tested)
strcat(str_buffer,":"); 
strcat(str_buffer,dec2ascii(read_min()));  //dec2ascii() returns ptr to "34"
strcat(str_buffer,":");
strcat(str_buffer,dec2ascii(read_sec()));
LCD_sendstring(str_buffer);