If you use
wget recursive download ability, or give it a list of files to get or both, you can use its
--wait option to give the same effect.
--wait=4 will add a pause of four seconds between each file meaning that you could get at most 900 files per hour (you would only get the 900/hour if each file transfer was instant though). If you know that each file will take more than 0.6 seconds to download you could use
--wait=3 which would be faster, obviously, but could break the 1000 files/hour limit (if each file transfer were instantaneous you could get 1200/hour).
wget is in the standard repositories for just about all Linux variants (and is often installed by default) and is available for Windows and other OSs too. It is a command line tool but there are many GUI front-end wrappers for it if you prefer (I can't recommend one personally as I always use wget from the command line).