Now it's worked once, it should lock on the sats faster in future. BUT whenever it's in 'searching for satellites' mode it will always be quicker if the BB isn't physically moving during that cycle, and has a reasonably clear view of the sky (not obsured by buildings and other dense things). The aquistion cycle needs to collect data from the satellites uniterrupted. The data rate is really slow, and it has to keep restarting if it gets interrupted (when you're moving there's likely a brief interruption as you lose the signal for a very short while, and there a "doppler" effect wich might get in the way too).
Once it has most of the data, it has to get less in future so aquistion is shorter, all being well. The data ages over time. After a week or two of non-use it takes longer again. Also if you move (100's? or) 1000's miles it can take a very long time again the first time you use it in the new location. It's all about the reveiver working out where the satellites are in the sky/their status and how to 'find' them again. Remember, relative to us, the satellites are moving.
This is a general GPS thing. I have a TomTom SatNav in my car. It can take 10mins or more to get a satellite lock if I switch it on whilst driving or even walking with it. It takes seconds if I do it before I set off...
The article below is very old and GPS tech has improved a lot since - but read this to get some idea what the receiver has to accomplish - it's a wonder anyone really believed it would work at all, and it's all going on in a chipset that costs a few dollars in your BB!! How a GPS Receiver Locks