I just got an N810 five days ago, and have observed the following about the GPS:

1. When Map starts, the GPS screen always displays "No GPS Connection" for about five seconds. Then it displays the globe with no satellites for about 10 more seconds.

2. 15-20 seconds after starting, the GPS screen first shows some satellites.

3. The amount of time it takes to lock into a position generally varies with the battery's state of charge. With a good charge it can be 30 seconds. With a low charge it's more like 45 seconds.

4. A couple of times it didn't get a fix at all. At one time it wasn't even seeing satellites. This seems to happen with the battery very low.

5. Warm start: Once it's got a fix, if the Map program is closed and reopened, it takes the same 15-20 seconds described in (1-2) above to start receiving satellites. Then it takes between four and 30 seconds more to reacquire the fix. It takes longer if the charge is low.

All my trials were with WiFi connected, no Bluetooth, and (I think) nothing else running.