To find out how many tasks are created and who created them on specific days of the week: 

1. Create the following Task / Custom Field Value script

Calendar ca = task.getSubmitdate();
ca.setTimeZone(TimeZone.getTimeZone(sc.getTimezone()));
int day = ca.get(Calendar.DAY_OF_WEEK);
switch (day){
     case Calendar.SUNDAY: return "Sunday";
     case Calendar.MONDAY: return "Monday";
     case Calendar.TUESDAY: return "Tuesday";
     case Calendar.WEDNESDAY: return "Wednesday";
     case Calendar.THURSDAY: return "Thursday";
     case Calendar.FRIDAY: return "Friday";
     case Calendar.SATURDAY: return "Saturday";
}
return null;

2. Create the calculated custom field submitdate of type List, based on this script. The list of possible element values must correspond to the list of possible results of the formula calculation (Sunday, Monday, etc). This calculated field returns the name of the day of the week when the task was created. 

3. Create the following report: