Why so long to retry candidate?

[cs3007uk]

Think I might know what is my problem as in my previous post.

I might get 3-4 files from the same candidate, then all of a sudden the status shows waiting 15 minutes to retry, but if I hit retry candidate it will resume downloading again.

So, two things:-

1) Why does it have to wait 15 minutes and what causes this?

2) Can I alter the retry time, so it will try again after like 5 secs rather than 15 mins?

Thanks