I would install the 13.10 version of Ubuntu as it has the most features and is the most up-to-date.
The other option would be to go with the 12.04 release.
This is the "Long Term Support" version and is a solid release but it does not have all the newest, cutting-edge features.
This is an add-on for the Advanced Custom Fields Word Press plugin, that allows you to add a Date and Time Picker field type.
This add-on will work with ACF 3 and 4 This add-on can be treated as both a WP plugin and a theme include.
The plugin is also available from the Word Press plugin directory Install as Plugin 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.
This section describes the functions that can be used to manipulate temporal values.