Google will be granting invitations to Inbox, its new cross-platform app for Gmail, during a one-hour window later today. If you've wanted an invite but have come up empty-handed so far, here's how to get a guaranteed invite.

It's simple really. All you need to do is send an e-mail to between the hours of 3 p.m. and 4 p.m. PT. Do that and Google promises to get you an invite by 5 p.m.

Hopefully, Google's servers will hold up under the load but I wouldn't hold my breath. It seems as though anytime something that's highly anticipated launches, like a new game or even a smartphone pre-order, the backend servers inevitably crumble under the load.

For those not up to speed, Inbox is Google's new app for Android and iOS that's designed to help manage your Gmail account. It takes the social network notifications, newsletters, bills, reminders, invitations and so on that can quickly clutter up your inbox and organizes them into neat groups called Bundles.

The app can also sniff out and highlight important information in your messages like flight itineraries, event information and photos. Inbox Assistant takes it one step further by adding relevant information to important messages such as status updates on flights or package delivery details.

No word yet on when Google plans to open the app up to everyone although today's limited invite window suggests they're certainly ready to bring more users onboard.