I'm currently doing a complete run of Bleach, along with the movies and the OVA, and I'm trying to figure out the complete timeline of it all. I know that there was already a question on here about when the movies were in relation to the anime (and a subsequent answer to that question), but I still don't know when the OVA is in relation to it all. Here's what I DO know (along with my assumptions based on that knowledge), in case it helps at all: The Bleach OVA is a special flashback episode that has to do with Ichigo's fight against Grande Fisher. However, Ichigo's father killed Grande Fisher in the Arrancar arc. So does that mean that it takes place some time before that?
...shown in Japan at the Jump Festa 2004 Anime Tour, is a pilot episode for the series. It focuses more on Ichigo's feelings regarding his mother's death. Tite Kubo, the creator of Bleach, voices Kon in this special instead of Mitsuaki Madono, the original voice actor of Kon. The closing theme used for the episode is "Memories in the Rain" by Morita Masakazu, the voice actor of Ichigo Kurosaki, and Orikasa Fumiko, the voice actress of Rukia Kuchiki. (Alternative version of episodes 8 and 9; watched best after episode 7)
Just to add, for the other OVA, The Sealed Sword Frenzy
It appears to take place soon after the Soul Society arc.
Which means that it's set after the events of Episode 63.