When creating HubSpot site or landing pages, you can certainly save and leave them in draft mode if you do not wish to publish them right away. Within the page's editor, you'll see a Save button towards the top right corner. Clicking on this button ensures all your edits are saved.
When you're done, simply navigate to another area of HubSpot or close your browser window. The page is already in draft mode and ready for publishing at a later time.