> I need to download  e.g. 500 URLs
> I do not want to hammer them. Can I slow down spider with 
> some sleep (10 min.)
> 10 min. is time for access the URL

1 link per 1 minute == 1 link per 600 seconds == 1/600 
links per second == 0.0017 links per second

Hence, go in
Set Options / Limits / Max connections per seconds

and type in "0.0017" (without the quotes)

Note: Use at least 3.33-RC5 (previous releases did not 
handle correctly floating number of connection)