Sales invoice during Ramadan

Use this Client script ,

frappe.ui.form.on('Sales Invoice', {

  onload: function(frm) {

    // Get the current date and time

    var currentDate = new Date();

    var currentHour = currentDate.getHours();

    // Check if the current time is between 12:00 AM and 3:00 AM

    if (currentHour >= 12 && currentHour <= 3) {

      // Subtract one day from the current date

      currentDate.setDate(currentDate.getDate() - 1);

    }

    // Format the date as 'YYYY-MM-DD'

    var formattedDate = currentDate.toISOString().split('T')[0];

    // Set the posting date

    frm.set_value('posting_date', formattedDate);

  }

});

Also , dont forget to tick "Edit posting date and time"

The same script with minor changes can be applied on other doctypes.