Hi Siobhan,
We use FTP to send our records to EDS. ByWater Solutions, our Koha support company, set up a cron job that sends our complete catalog to our EBSCO FTP site every night at midnight. I get an auto email from EBSCO whenever the file is processed. Sometimes they get the records processed by 6 or 7 in the morning; sometimes it isn't processed until the afternoon. I guess it depends on the sever load on any given day and how many other files it has to process.
As I recall, we set it up this way because we were having a similar problem with trying to send information to EDS about which records needed to be deleted and which ones are added. With this solution the catalog is rebuilt every day.
If you'd like more details, I could look into our settings for you. Maybe send you some screenshots. Would that be helpful?
As for RTAC, I don't think we've turned that on. I remember it not being very accurate and slowing down the load time for search results. That is why we have been working so hard to de-bug Discovery searching in the Koha interface because when you use the EDS plugin for Koha the availability displays natively in Koha.
Myka