The Date input block allows you to ask your user for a date. You can ask for a specific date or range and include time:
Date input in flow
The input will use the native date picker depending on the device and browser used to answer the bot. For example on Firefox it looks like this:
Date native picker

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Format

The Format setting lets you customize the picked date format. Under the hood, it is done using the date-fns library. You can use any of the formatting tokens supported by the library. Here are some examples: 
yyyy-MM-dd
yyyy-MM-dd HH:mm:ss
dd/MM/yy
dd/MM/yyyy HH:mm:ss
d.MM.yy