If you're the owner of the spreadsheet, you can publish it to the Web at any time. If you'd like to allow your collaborators to publish spreadsheets, make sure the option labeled 'Editors will be allowed to add people and change the permissions' at the bottom of the 'Sharing settings' window is selected (otherwise, click Change to change it). Collaborators can then publish, invite others to edit or view the spreadsheet, forward invitations to mailing lists, and see who else has viewing or editing permissions.
If the option 'Editors will be allowed to add people and change the permissions' isn't selected, collaborators won't see Publish as web page... in their sharing menu.
Note: people with only viewing access can't publish.