I PERSONALLY, would not leave mine without a sitter for more than 14 hours (or overnight--post bed-time)-granted, she is a cockatoo and they are kind of extreme...That is not to say that bird owners never do... Mine gets covered and uncovered on a schedule and she also needs her water changed etc. Plus, she needs to get out of her cage at least 1x daily for 3 hours MINIMUM, so this would never be possible in my world, even though I wish it were. She is independent as cockatoos go, but she still gets herself into trouble, and she is so in need of social interaction, so I just wouldn't be comfortable leaving her that long...at least, at night, she is generally sleeping, but in the daytime, she does weird stuff sometimes and so it is (in my opinion) important to be aware that they could get tangled or stuck etc.
Don't get me wrong, I work-- but I just can't imagine her waiting and waiting for me to come home and no one ever coming to cover her, and no one ever coming to feed her dinner...I know my bird PERSONALLY would be very upset by the isolation, but again....cockatoo vs. other parrots may be the difference.