My understanding is that a new road surface takes a year to get fully up to friction.
Basically, the stones provide the friction, the tar is just there to hold the stones in place. When a new surface is laid, though, the stones are covered in tar. They come good when the surface tar is fully worn away by traffic which takes about a year of use, obviously dependant on the use.
When the surface gets laid, it's not dangerous, the uneven surface means that it offers more grip than over-banding, but it doesn't offer as much grip as it will give in 12 months, so I'd just take it a touch easier for a while.