That's a statistics we don't have right now. I'd need to write a small perl script to analize the logs and see what's the average delay is. I'm suffering from it too, because I use sg for daily email.
The only way to deal with that is more resources, which means a commercial service. See
http://www.spamgourmet.com/bbs/viewtopic.php?t=411. Right now, the response is quite underwhelming, so I guess we'll all have to accept the inherent poor performace of a free service.
Again, if there was an entrepreneir who wanted to set up a for-pay instance of spamgourmet somewhere using our GPLed code, I'd enthusiastically buy an account for my critical email, and SG would of course keep operating.