There are two ways to create multi-day options for polls:
With dates AND specific times:
To create multi-day options with times, you have to view the poll in week view (check this at the top of the poll). Start by clicking on the start time of the first day. Then grab the bottom of the blue box and drag it into the next day. Let it go at the end time of the event. You can do this again for another day. It is not possible to create overlapping multi-day events with times.
The result will look like this
With dates and no specific times:
If you need multi-day events without times specific times, you can use the free text option 'survey": https://doodle.com/create-choice/