...Under normal circumstances, Yorkies have 'permanent up' ears. They are down (floppy) from birth basically and then go through a stage of ''up and down'' or ''one up and one down'' for a month [at 3 months] and finally they stay ''perked up'' usually at 4-5 months.
All dogs are different and may be earlier or late bloomers. (My Daisy was a late bloomer
) Her ears went up and stayed up at around 5 months.
Here are pics of Daisy and her ears when she was ~3 months, in between, and 5 months.