I think it depends on your hospital trust. I pushed the sonographer after the scan and she said that the nuchal fold measurement was "within the normal range" but wouldn't tell me what it was, and said it would go into analgorithm with other results before we would be told our risk level. I the had my blood taken, which gets sent away to Cambridge for analysis. I got a letter about 6 days later saying I was low risk- if they'd found anything worrying, they said they'd call me within 48 hours of the blood being taken.
Yes it depends. If I remember rightly we were told it could take up to 4 weeks to get our screening results back (I don't think that's particularly normal though). They should at least be able to tell your your NT measurement is ok from the scan. As PP said, if it's high risk they'd get back to you quite quickly though - I got a call after 3 working days (high risk from the bloods but all was ok).