I don't know, but I really would love to stop that delay AND be able to subscribe immediately. Thanks for bringing this up, as I assume someone will have an answer.
> Why is there such a delay in Google Groups anyway, does
> anyone know?
Google Groups grew out of Usenet News which uses the NNTP protocol. This is a "pull" rather than "push" protocol. Google Groups still interfaces with Usenet, so I guess that Google Groups still uses NNTP to synchronise. Maybe they "pull" once or twice a minute.
Nice to see the first posts in October in the blog now.