I have products that are on QVC tomorrow, but the wbsite is running likea pig and the developer is not available at weekends, I was thinking of running the Flush Storage as I have re indexed the index's
No, it will slow down the site at least for a while, until the cache is warmed up again, because no content can be fetched from cache and all content has to be generated from database and XML files again.
As an example, opening a product page after flushing the cache often takes several seconds. The second time when everything is cached, it's typically down to 100-200ms
So, immediately before expected increase in traffic, it is quite a bad idea. You should only do it if you are worried about outdated content.