I made a simple Custom Indicator for your case - Time Grid.

The day / Time periods are pre-programmed, but it is very easy to be changed.

The core of the indicator code:

// Calculation of the logic
for (int bar = firstBar; bar < Bars; bar++)
{
    int hour = Time[bar].Hour;
    switch(Time[bar].DayOfWeek)
    {
        case DayOfWeek.Monday    :
        case DayOfWeek.Tuesday   :
        case DayOfWeek.Wednesday :
        case DayOfWeek.Thursday  :
            signals[bar] = ((hour >= 6  && hour < 13) ||
                            (hour >= 17 && hour < 19) ||
                            (hour >= 22 && hour < 23)) ? 1 : 0;
            break;
        case DayOfWeek.Friday :
            signals[bar] = ((hour >= 6  && hour < 13) ||
                            (hour >= 17 && hour < 19)) ? 1 : 0;
            break;
        case DayOfWeek.Saturday :
        case DayOfWeek.Sunday   :
            signals[bar] = 0;
            break;
    }
}

Thank you Popov!

Open it in any text editor. Preferably Notepad++

These cases are labels that separate the days of week. If you have several labels, all execute the same code.

case DayOfWeek.Monday    :

You can put conditions between the label if you want. Every condition finishes with "break;". If you miss the "break;" the program will continue with the next label.

For example the following code allows entries from 8:00 to 20:00 from Monday to Thursday and from 8:00 to 12:00 for Friday.

    switch(Time[bar].DayOfWeek)
    {
        case DayOfWeek.Monday    :
        case DayOfWeek.Tuesday   :
        case DayOfWeek.Wednesday :
        case DayOfWeek.Thursday  :
            values[bar] = (hour >= 8  && hour < 20) ? 1 : 0;
            break;
        case DayOfWeek.Friday :
            values[bar] = (hour >= 8  && hour < 12) ? 1 : 0;
            break;
        case DayOfWeek.Saturday :
        case DayOfWeek.Sunday   :
            values[bar] = 0;
            break;
    }

This message shows you that the indicator is already loaded from the original file TimeGrid.cs

If you want to use your version together with the original, you have to rename the class and the constructor, and the indicator name text.

    public class TimeGridProva : Indicator
    {
        public TimeGridProva()
        {
            IndicatorName     = "Time Grid Prova";
            PossibleSlots     = SlotTypes.OpenFilter;

Clean the Library folder. The old dll causes the conflict.

The problem is that there is no MQL version of the indicator. I'll make it this evening or tomorrow.

I added MQL version of the indicator to my first answer.
I made also minor changes in the CS code in order to make it looking as the MQL code.

You have to use both file.
Put the .cs file in "C:\Program Files\Forex Strategy Builder Pro\User Files\Indicators"
And the .mqh file in "C:\Program Files\Forex Strategy Builder Pro\User Files\MT4 Files\MQL\Forexsb.com\Custom"

The first one is used in FSB and the second one in the exported Expert Advisors.
If you want modifications, you have to modify both files in order to achieve the same results in MetaTrader.

I think you might be using your own modified indi with a different name (Time Grid Prova vs Time Grid), but it doesn't work because the naming is different between .cs and .mqh. Please add the error message itself also, then we don't have to guess what error is about.