Obtain the minute difference between the values of 2 DateTimePicker controls [closed]

I try to get the minute difference in TextBox with two controls DateTimePicker .

When compiling the program for the first time it shows me a very long number, then when changing the time in the control, it does show me the time.

This code is being executed in the event ValueChanged of each DateTimePicker . That is, it is found as such in each of the 2 events, but it is strange because it only happens when I execute it initially.

DateTime horaInicio = dtpHorainicial.Value;
DateTime horaFinal = dtpHorafinal.Value;

// A la hora final le restamos la hora de inicio
TimeSpan diferencia = horaFinal.Subtract(horaInicio);

// Mostramos la diferencia en un control TextBox
txt_tiempoTotal.Text = $"{diferencia.TotalMinutes} Minutos";