Convert hour 24 hours to 00 hours

I have an account in int, i need to return it for hours, and it is working perfectly, the error occurs when the time appears 24, and it should appear 00: 00. Here's how I'm doing:

string horaStg;
decimal valor = int.Parse(item.HoraInicio);
valor = (valor / 60);
var inicio = valor.ToString().Split(char.Parse(","));
string hora = inicio[0];
try
{
    string minuto = "0," + inicio[1];
    string m = Math.Round(decimal.Parse(minuto.ToString()) * 60).ToString();
    horaStg = DateTime.Parse(hora + ":" + m.Substring(0, 2)).ToString("HH:mm");
}
catch
{
    horaStg = DateTime.Parse(hora + ":" + "00").ToString("HH:mm");
}

How can I convert to appear at 00:00 ? For the way it is when it is midnight, it appears 24 and returns me the following error:

The DateTime represented by the string is not supported in calendar System.Globalization.GregorianCalendar.

I made an if, like this:

if (hora == "24")
{
    hora = "00";
}

But don't you have any conversion that you do directly ?