A workaround for Xamarin.Android date/time format bug https://bugzilla.xamarin.com/show_bug.cgi?id=23544

DateTimeFormat.cs

public static class DateTimeFormat {
    public static bool Is24Hour {
        get { return CultureInfo.CurrentCulture.DateTimeFormat.LongTimePattern.Contains("H"); }
    }
}

SplashScreen.cs

public class SplashScreen : Activity {
	protected override void OnCreate(Bundle bundle) {
	    base.OnCreate(bundle);
		
        try {
            var shouldBe24Hour = DateFormat.Is24HourFormat(this);
            var monoIs24Hour = DateTimeFormat.Is24Hour;
            
            if (shouldBe24Hour && !monoIs24Hour) {
                var newCultureInfo = new CultureInfo(CultureInfo.CurrentCulture.Name);
                var newUiCultureInfo = new CultureInfo(CultureInfo.CurrentUICulture.Name);
            
                Ensure24Hours(newCultureInfo.DateTimeFormat);
                Ensure24Hours(newUiCultureInfo.DateTimeFormat);
            
                Thread.CurrentThread.CurrentCulture = newCultureInfo;
                Thread.CurrentThread.CurrentUICulture = newUiCultureInfo;
                CultureInfo.DefaultThreadCurrentCulture = newCultureInfo;
                CultureInfo.DefaultThreadCurrentUICulture = newUiCultureInfo;
            }
            else if (!shouldBe24Hour && monoIs24Hour) {
                var newCultureInfo = new CultureInfo(CultureInfo.CurrentCulture.Name);
                var newUiCultureInfo = new CultureInfo(CultureInfo.CurrentUICulture.Name);
            
                Ensure12Hours(newCultureInfo.DateTimeFormat);
                Ensure12Hours(newUiCultureInfo.DateTimeFormat);
            
                Thread.CurrentThread.CurrentCulture = newCultureInfo;
                Thread.CurrentThread.CurrentUICulture = newUiCultureInfo;
                CultureInfo.DefaultThreadCurrentCulture = newCultureInfo;
                CultureInfo.DefaultThreadCurrentUICulture = newUiCultureInfo;
            }
        }
        // ReSharper disable once EmptyGeneralCatchClause
        catch {}
    }
    
    private void Ensure24Hours(DateTimeFormatInfo dtf) {
        dtf.LongTimePattern = "HH:mm:ss";
        dtf.ShortTimePattern = "HH:mm";

        var index = dtf.FullDateTimePattern.IndexOf("h", StringComparison.Ordinal);

        if (index > -1) {
            dtf.FullDateTimePattern = dtf.FullDateTimePattern.Substring(0, index) + dtf.LongTimePattern;
        }
    }

    private void Ensure12Hours(DateTimeFormatInfo dtf) {
        dtf.LongTimePattern = "h:mm:ss tt";
        dtf.ShortTimePattern = "h:mm tt";

        var index = dtf.FullDateTimePattern.IndexOf("H", StringComparison.Ordinal);

        if (index > -1) {
            dtf.FullDateTimePattern = dtf.FullDateTimePattern.Substring(0, index) + dtf.LongTimePattern;
        }
    }
}