Just to close the loop:
I did the flights today. Based on the feedback received in this thread, I used 2 of my vouchers to upgrade to business class (yes, I know - but I can't use them anyway otherwise). Even more so when I called Aegean for the upgrade, and the lady told me "Sir, haven't you been informed that your flights have been cancelled" ? Errrr.... no !
Seems they changed the times for summer schedule. No big deal, they re-booked me, but my transit time came down to 35 mins.

However - no issue: as described, got the business class bus in SKG (was actually alone in there, as the 2 other people in business class were the patriarch of Athens and one of his colleagues - so they had their own bus), and made the chain bus - exit - departure floor - security (got the fast lane) - lounge in less than 10 mins. Even had 15 mins of time then in the lounge to sip a coffee.
I guess I could have made even with being in economy (although the flight was full).

Thanks everyone for the hints and I hope this serves for someone who thinks about doing the same.