Thanks all for your help unitl so far.
So, I tried your solution David but it didn't work. Or I didn't make it work I don't know
This is a sample of the data in the source
21/Dec/12 2:17 PM
21/Dec/12 1:04 PM
21/Dec/12 5:46 PM
I don't know how to convert the hour, so still with a derived column, I just kept the date. Now I'm trying to convert it as dd/mm/yyyy...
I have a lot of datas, not juste 3, and I have to do an automatic task, so I don't think your solution is fine for this problem. But thank you
By the way, sorry for my poor english