It seems to vary a great deal from person to person, some people say it works in minutes while for others it takes tens of minutes.

But as with any GPS unit, do NOT try to get a fix while still indoors. Go outside before you try to get a satellite fix.

However, it has to be said that the N810's GPS unit is not very good. I did a comparison with some of Nokia's GPS-equipped smartphones (including the similarly-sized E90) and they were much much much faster at getting a fix (and it wasn't assisted GPS by the way).