A workaround for a bug in Mono for DateTime.Now for people who also use MvvmCross.

DateTimeEx.cs

public static class DateTimeEx {
    private static IDateTimeProvider _provider;

    public static DateTime Now {
        get {
            if (_provider == null && !Mvx.TryResolve(out _provider)) {
                return DateTime.Now;
            }

            return _provider.Now;
        }
    }

    public static DateTime Today {
        get { return Now.Date; }
    }

    public static DateTime ToUniversalTimeEx(this DateTime dt) {
        if (dt.Kind == DateTimeKind.Utc) {
            return dt;
        }

        return dt.Add(DateTime.UtcNow - Now);
    }
}

public interface IDateTimeProvider {
    DateTime Now { get; }
}

DroidDateTimeProvider.cs

public sealed class DroidDateTimeProvider : IDateTimeProvider {
    public DateTime Now {
        get {
            var c = Calendar.Instance;

            return new DateTime(
                c.Get(CalendarField.Year),
                c.Get(CalendarField.Month) + 1,
                c.Get(CalendarField.DayOfMonth),
                c.Get(CalendarField.HourOfDay),
                c.Get(CalendarField.Minute),
                c.Get(CalendarField.Second),
                c.Get(CalendarField.Millisecond),
                DateTimeKind.Local
            );
        }
    }
}

iOSDateTimeProvider.cs

public sealed class iOSDateTimeProvider : IDateTimeProvider {
    public DateTime Now {
        get { return NSDate.Now; }
    }
}