Although it's far from ideal, especially given that you appear to have a lot of listings at the time of typing this response, one workaround solution that you could use until such time as eBay sort the problem out and put it right would be to revise your listings and include a line on each saying something along the lines of "Please be aware that there is currently a glitch on the site providing unrealistic despatch times. Items for which payment has been received will be despatched within [insert number here] working days". If you add the text to the item description in bold type, a larger typeface and in an eyecatching colour, such as blood red, then hopefully any potential buyers who may otherwise have been put off of making a purchase will spot this extra note in the item description and decide to make a purchase anyway.
If you do decide to give this a shot then once you have despatched any goods sold add the tracking number(s) to the relevant listing(s) and perhaps even send your buyer a quick e-mail via eBay Messages, saying something along the lines of "Thank you for your purchase. Your item has been posted to you today via [enter postal service used here] and ought to be with you within [insert number here] working days". By keeping your buyers informed of the fact that you have despatched the items purchased it should help to reassure them that you are doing your best to ensure that they receive their items within an acceptable timeframe.
