According to this post, there's a separate DatePicker control in .net 4. I've tried it, and I don't see a good way to also let it select the time of the day.
Is there an easy way to transform DatePicker into DateTimePicker by editing XAML template? If not, what is the best way to get a DateTimePicker for WPF 4.0?
Extended WPF Toolkit sports a nice DateTimePicker with time of day.
There is also an article over on CP where someone created a control that works like the Winforms one... A WPF DateTimePicker That Works Like the One in Winforms