Just like Super Aurora said, I believe Cinderella is actually more in the 1700's style of clothes and hair, possibly even very late 1600's (when Perrault wrote Cinderella) since a lot of that kind of fashion started then.
Cinderella's pink gown and even her hair looks kind of like this 1700's fashion plate:

The sleeves in this first picture kind of look like Cinderella's, as do the hair and width of the gown of the girl in the second look like Cinderella's, and they're both from the 1700's:

The hair and choker necklace of the girl in this late 1700's painting look a lot like Cinderella's:

And I think this woman really looks like Cinderella, during the 1700's which was the reign of XV, and one of the Disney background artists said they made the architecture in the film look like from that of Louis XIV:

There are also some pictures from the late 1600's to the 1700's that look a lot like Lady Tremaine's fashions:

But I have to admit, this next picture from the middle of the 1800's looks so much like Cinderella (in red) and Lady Tremaine (in purple):

And then there's the Prince, who I must admit, like all the other men, looks like he's wearing clothes from the 1800's. He especially looks like this Prince of Austria, the picture's from somewhere in the 1840's to 1850's:

But the men sometimes have the knickers, jackets, wigs and tricorner hats that are very much from the 1700's or late 1600's. Usually the men of high status but who are servants to people in higher status, like Cinderella's dog Bruno made her footmen and the Duke's slipper fitter:

So I think the film could be set anywhere from the very late 1600's to the 1700's to the 1800's, just with costumes that look like ones from any of those eras, and I'd like to think it's the late 1600's when Perrault originally wrote his tale, but some people think any clothes past that date must mean its set later. I disagree, but you can think for yourself. I'd like to think they just *happened* to make clothes that just *happened* to uncannily look like in some ways like clothes from the future. They were ahead of their time! lol