Define a summary field to compute the average of your elapsed time field.
If you perform a find for all records with today's creation date, this summary field will compute the average time spent on each record.
Create a self join relationship linking this table to itself by creation date. This will look like you have two tables, but you'll only have one table with two "boxes" (table occurrences) to the same table in Manage | Database | Relationships
Open Manage | Database | Relationships, select your table and click the button with two green plus signs to create a second table occurrence of your table. Link them by your creation date field. Let's name this second occurrence "SameDate".
Click the fields tab and define a calculation field with this expression to compute the average: Average ( SameDate::YourTimeIntervalField )
Now you can see the average time for a given date on any record created on that date.