ahem... I must confess I even had to look up what a 'turn' is....

Does this help:
http://www.questionthesanity.com/inverted_tern.jpg

Where the curl of a turn is pointing downwards, this is an inverted turn. There are at least three ways of showing an inverted turn:

(a) As a standard turn only with a short vertical line through the middle.
(b) As a standard turn only the other way around ie with the first curl pointing upwards and the end curl pointing downwards.
(c) Like a standard turn only written vertical instead of horizontal.

These ornaments are not seen that often as they are usually written out in full. I realise your particular example is Chopin, but, in general, the speed the turn is played depends on the tempo of the music and the note values indicated by the composer in relation to the time signature. My old professor also argued that the period of the music also has a bearing on this.

In the case of an inverted turn, the note below the principal note is played first