DD has definitely started this. She started at about 6.5 months when I did a first aid course for a weekend and was gone 6-7 hours a day.
She's been having trouble with going to sleep since (she doesn't like to be away from me), so we let her fall asleep next to us on the couch and bring her upstairs then. She gets upset if she can't see us at all times. Her crib is still in our room, but her bedtime is earlier than ours.