Are you updated to CS5 5.0.3? Are the P2 files (I'm assuming that's what they are) on a local drive? Do you have the P2 folder open in the Media Browser?
The Media Browser is an interesting question. The browser works but does not see the Avid Unity drive I must use to store edit media. This is a fiber optic system that media has to live on to share with other Avid editors. The Browser can see other volumes on the computer and on Ethernet servers. I did do a test on a local drive and still had the delay.
If you're saying you're on CS5 5.0.0, go to Help > Updates and get up to 5.0.3, then test the delay. Some of these issues were addressed in the updates.
I am up todate, 5.0.3
I did open my test project with the quicktimes of the same media on the Avid Unity drive and no delay in start up. It must be due to the structure of the MXF files being build by different files, like video, audio and such. I did not like the quicktimes because the gama changed and I lost timecode, each clip started at 00:00:00. I made the quicktimes with Adobe Media Encoder. Should I make AVI's? If so what are codac, lossless?