Hi Pinmaya,
You can create your own business rule if an existing one does not fit. If you are not familiar with how to do this I would suggest reading the available training documentation and potentially arranging for specific Business Rule training. It is a very good idea to get a full understanding of the business rule functionality delivered from an expert in the area as it is a very versatile area of the system.
To check the day you would just need to select a field from the task that contains the date you wish to compare against and then put the condition in as comparing it to todays date. If such a field does not exist you can use a user_def field and another business rule to complete the field with the date at the relevant time. As you can see this would then be a chain of business rules which can then get a little complicated which is why I would suggest the Business Rule general training first so you have a good understanding going in.
Kind regards,
Lee Pinchbeck