This is called Cold start - if the GPS not been used for a long time and/or has moved several hundred kilometres it will take some time to get the first fix.
In this state, the GPS receiver does not have a current almanac, ephemeris, and initial position.To determine the location of the GPS satellites two types of data are required by the GPS receiver: the almanac and the ephemeris. This data is continuously transmitted by the GPS satellites and your GPS receiver collects and stores this data.
To get a fix, your GPS receiver requires additional data for each satellite, called the ephemeris. This data gives very precise information about the orbit of each satellite. Your GPS receiver can use the ephemeris data to calculate the location of a satellite to with a metre or two. The ephemeris is updated every 2 hours and is usually valid for 4 hours.
Even if your GPS receiver has been off for a while, it may take up to several minutes to receive the ephemeris data from each satellite, before it can get a fix.
When Nuvi must recreate its almanac, it needs probably around one minute per satellite. So to get a new position it will need at least 4 minutes and to get a precise one probably around 15 minutes.
"Cold/warm/hot start" indicate how many pieces of data the GPS receiver already has.
Warm start - current almanac, initial position, and time are all valid. Ephemeris data is either invalid or only partially valid. Time-to-first-fix is likely to be 30 seconds to 2 minutes depending on satellite availability and the type of GPS receiver.
Hot start - if the receiver has been off for, say, less than an hour time-to-first-fix will likely be 5-20 seconds.