The 500 only uses the american GPS satellites and as such there are not near as many and it takes longer to lock on enough for the unit to read a position. The 1000 on the other hand uses american gps satellites and the Russian glonass satellites so there are quite a few more to lock into so it is quicker. I also think the 1000's technology is faster in satellite acquisition.The 500's technology is about 5 years old, while the 1000's technology is about a year old.
I have owned both units. The 500 typically took about 90 seconds if I was outside and not moving. If I was moving or was inside it may take 4-8 minutes.
The 1000 locks on in about 10-15 seconds outside or inside it really doesn't make any difference. Garmin has really stepped up its game on the 1000. I bought mine about 5 months ago so I never had the issues with the firmware that hat lots of bugs and problems. My unit has been rock solid from day one.