Yes, definitely. RAID systems are fragmenting often even worse than normal hard disks, because files are scattered around the disks (depending on the RAID level used). Thus, fragmentation becomes an important performance issue.
You should allow your configuration at least 2 hours, if you never did a defrag before. However, this is depending on your config. If you have lots of small files, it might take longer. If you have lots of large files, but continous space is rare, the defragger must move files out of the way, which takes additional time.
This was first published in February 2002