It was the just the same when I was using Turbo Lister.
All my checkout and invoicing I do directly through eBay, that suffers too.
Personally I would not list on Sunday or Monday regardless, if you want items to end on a Sunday fine most do, then post for 3, 5 or 10 days, never 7.
You could write the listings during the week and schedule items to be posted from Auctiva on Sunday, but they may still get delayed or time out (default is to retry for 30 minutes).
The preferred end date and time can be very item specific just like TV adverts which are targetted for specific age groups at specific times of the day and within specific TV programmes.
You need to experiment but try and avoid the eBay rush 'hours'.
