Thanks to Fals, it's now working with :
<div class="form-group">
@Html.LabelFor(model => model.Days, new { @class = "control-label col-md-2" })
<div class="col-md-10">
@Html.EditorFor(model => model.Days, "Day")
@Html.ValidationMessageFor(model => model.Days)
</div>
</div>
To display the textbox as a HTML5 DatePicker, don't forget to add a DateTime.cshtml in the EditorTemplates with the following code (type of your day field must be DateTime) :
@model Nullable<DateTime>
@{
DateTime dt = DateTime.Now;
if (Model != null)
{
dt = (System.DateTime)Model;
}
@Html.TextBox("", String.Format("{0:d}", dt.ToShortDateString()), new { @class = "form-control datecontrol", type = "date" })
}
Source : http://www.aubrett.com/InformationTechnology/WebDevelopment/MVC/DatePickerMVC5.aspx(