Google is expanding its Inbox invite program, having issued another collection of invites to existing members already today, with a new ‘Happy Hour’ taking place between 3 p.m. PT and 4 p.m. PT today. If users email them at inbox@google.com asking for an invite during that window, they’ll get access guaranteed by 5 p.m. PT today.

Want an invite TODAY? #InboxHappyHour 3-4pm PT. Send us an email at inbox@google.com between 3 and 4pm PT and you'll get your invite by 5pm — Inbox by Gmail (@inboxbygmail) November 5, 2014

If you’re still waiting for access, this is the most certain method yet for locking in an invite. Keep in mind that only personal Gmail accounts can access the Inbox while in beta, so even if your work email is run through Google Apps, you won’t be able to sign up, at least for the time being.

Google’s Inbox is the app that has proven the most interesting for me thus far in terms of non-traditional email software, after other entrants including Mailbox failed to really light a fire in my belly. The app benefits by machine learning smarts that Google began developing and honed using its smart Categories feature for standard Gmail, and in its Google Now intelligent mobile assistant software.