You cannot specify a Date field as the record title.
Fields that can be specified as the record title are as follows:

• Record number
• Text
• Text area
• Rich text
• Number
• Calculated
• Lookup

As an alternative, you can use a "Calculated" or "Text" field, which can be specified as the record title, to display the content of the "Date" field as the record title.
To do so, you need to set a formula to display the content of the "Date" field in the "Calculated" or "Text" field, and then specify the field as the record title.
The steps are as follows.

1. Check the field code of the "Date" field you want to display as the record title.

2. Place a "Calculated" field, then click Settings from the gear-shaped Settings icon at the top right of the field.

3. Enter the field code of the "Date" field, which you have checked in Step 1, in the "Formula" input field.
   Select "Date (Aug 06, 2012)" as the display format and click Save.

4. Click Save Form on the upper left side of the screen.

5. Specify the "Calculated" field as the title field.
   Setting Title Field

Update the app. You have successfully configured the setting.

To display the content of the "Date" field in a "Text" field, you need to use the "DATE_FORMAT" function.

1. Check the field code of the "Date" field you want to display as the record title.

2. Place a "Text" field, then click Settings from the gear-shaped Settings icon at the top right of the field.

3. Select the Calculate automatically check box, enter a formula, and then click Save.
   For example, if the field code you have checked in Step 1 is "Date", the formula is as follows:
   DATE_FORMAT(Date,"YYYY-MM-dd","Etc/GMT")
   DATE_FORMAT Function: Specifying the Display Format of Date and Time
   

4. Click Save Form on the upper left side of the screen.

5. Specify the "Text" field as the title field.
   Setting Title Field

Update the app. You have successfully configured the setting.