When you click New invitation you are presented with a weekly calendar grid on which you can propose times by clicking and dragging. There is no limit to the number of times that you can propose. You can drag across days and hours and quickly propose many times without any additional overhead.
 
However, when you propose times think about your invitees that will have to respond with their availability. Proposing too many times is not a good practice as it will require lots of work from the invitees.

If your Google Calendar is connected you can select the calendars that you want to display. By default, calendars display your busy times for information only and do not block your availability. If you want busy times from your calendars to block out your availability, check the “Busy time blocks my availability” box. See the Understanding busy time behavior article to learn more.

If your calendar is connected, when you click “Save and get invitee link” for the first time, a “ScheduleOnce proposed times” calendar will be created in your Google Calendar. See the ScheduleOnce proposed times calendar article to learn more.

Once you click "Save and get invitee link" you get the invitee link which you can copy and paste into your email to send out to your invitees. In your home page you will see the new outbound invitation that was added to your Active invitations list. From here you can edit it and make any required changes including adding or removing times. When you save your edits the link will not change, so there is no need to send it again to your invitees. See the Editing outbound invitations article for more information.

If you added more times for example, you can simply tell your invitees to click their link again and update their availability. Invitees will be able to edit their previous information and will not have to create a new entry.