It takes about 5 days, but I would not recommend it, unless you absolutely must have "blue box and ribbon" with "Tiffany" on it.
EU distance selling regulations doesn't not apply to the US sellers. Returning unwanted jewellery to the overseas seller is total nightmare.
And there is nothing special at Tiffany website, unless you are collector of Picasso or Schlumberger's pieces.
If you shopping for the jewellery in UK, try local sites. There are hundreds of quality jewellery sellers, for example:
1. Links of London ( great charms and some silver)
www.linksoflondon.com
2. Astley Clarke ( affordable designer jewellery )
www.astleyclarke.com/
3. Fameo ( fine jewellery and good selection of gemstone jewellery)
http://www.fameo.co.uk
4. Ernest Hones and H. Samuels ( wide range of affordable commerial jewellery)
www.ernestjones.co.uk