If you see this error message when you are creating your date poll, it is most likely because you have chosen some dates without time slots selected, and some other dates with specific times slots selected. Alternatively, it could also be because you have selected all your options without specific times and enabled a time zone. Then it is not possible for your poll to have a time zone.
In step 2, when you create the poll, make sure that you either have specific times on all days or none of the days. Click on the little "x" next to the times to delete them, or click "add times" to put in some specific times for the rest of the dates.
You can also click on the current timezone and then choose the very first option "remove timezone from this poll". Then you can make the poll with or without times as you would like.