Whether you can leave a bird alone during the day does depend on the bird. My lovebird actually got upset when I worked from home; apparently, I interfered with his afternoon nap. He'd start squawking pointedly at me around 1 and wouldn't stop until I left the room, whereupon he would tuck his beak into his back and sleep for three or four hours. The conure I have now likes to have me around during the day, but is fine if I'm not, as long as she gets a few hours of company and attention.