Date and Time Picker Field

Copy the 'acf-date_time_picker' folder into your plugins folder
Activate the plugin via the Plugins admin page

Include

Copy the 'acf-date_time_picker' folder into your theme folder (can use sub folders). You can place the folder anywhere inside the 'wp-content' directory
Edit your functions.php file and add the code below (Make sure the path is correct to include the acf-date_time_picker.php file)

add_action('acf/register_fields', 'my_register_fields');

function my_register_fields()
{
include_once('acf-date_time_picker/acf-date_time_picker.php');
}

Updating to ACF PRO
I got this quetion over at AWP on Facebook:

How does upgrading work? If someone starts with ACF and your plugin,
then upgrades to ACF Pro, will their date/time custom field disappear?
I understand the data will be maintained but wondering if the field
will still be visible in WP admin.

Updating to ACF PRO should work fine, ACF PRO has a compatibility add-on for this plugin, but test it on a non production environment first.

Also, read the comments on this issue: https://github.com/.../acf-field-date-time-picker/issues/103
How do I set the date and time format?
To set the date and time format when you create the field, you have to create a string using the letters below.
Date format
d day of month (no leading zero)
dd day of month (two digit)
o day of the year (no leading zeros)
oo day of the year (three digit)
D day name short
DD day name long
m month of year (no leading zero)
mm month of year (two digit)
M month name short
MM month name long
y year (two digit)
yy year (four digit)
Time format
H Hour with no leading 0 (24 hour)
HH Hour with leading 0 (24 hour)
h Hour with no leading 0 (12 hour)
hh Hour with leading 0 (12 hour)
m Minute with no leading 0
mm Minute with leading 0
s Second with no leading 0
ss Second with leading 0
l Milliseconds always with leading 0
t a or p for AM/PM
T A or P for AM/PM
tt am or pm for AM/PM
TT AM or PM for AM/PM
Examples

yy-mm-dd: 2013-04-12
HH:mm: 24 hour clock, with a leading 0 for hour and minute
h:m tt: 12 hour clock with am/pm, no leading 0

The Date and Time Picker field is saved as an UNIX timestamp. Use the PHP date function when you use it in your theme.