It can vary greatly. Rob will always post them promptly, but HM Customs can (literally) take as long as they like, but that technically implies to any import.
Typically, things I order from the US (quite a bit in fact
), take between one and two weeks on average. Occasionally it's a little more or less.
When buying from a US dealer, you should always factor in 15% of the value of the package, plus and 8GBP post office "handling fee" if customs decide you have to pay tax and duties. So if you buy a Juice for say, 50.00GBP incl. shipping, be prepared for additional fees of about 15GBP at your local sorting office! Often you'll get away with it, but if it's "correctly" labelled leaving the US, you should always factor that in.
Even if you do get stung, you'd struggle to find a NIB XE6 for 65GBP total in the UK, as people aren't allowed to sell them for that!
Feel free to PM me if you're unsure