It could have been a great day for Tiffany & Co. (NYSE: TIF) stock investors. Instead, it ended up being only a good day.In early trading Tuesday, Tiffany stock ran up 6.6% at first, as investors cheered the results of the company's most recent earnings quarter. For fiscal Q2 2018, Tiffany reported earning $1.17 per share on sales of $1.08 billion.