Datetime fields within a fact table

can we have a datetime column in a fact table?in which scenario's is this correct to have a datetime in a fact table.
In my Facttable i stored date as int.They are just the milestone dates reported against each activity.I show those dates in reports.
So i dont see a purpose in storing them as int and joining with DIM tables to get the dates.So wanted to make sure if i can have them stored as datetime.

Yes, that is fine. They would be degenerate dimensions.

Is there any particular rule as in a date field to be used as int? or to use as Datetime?

If you mean by 'as int' as a foreign key to the date dimension, it is when you need the attributes in the date dimension.

Got it
But my question is why would someone use a datetime or int in fact .If there is any filtering condition to be done in reports we go for int and
when we just have to show in a report we go as datetime?

Why would you convert a DATE column to an INTEGER column to support filtering? Filtering a DATE data type works, and you have more functionality to compare and manipulate values.

However, the point of having a date dimension is to provide this functionality without end-users needing to know date functions, such as knowing the date is a Tuesday or belongs in a particular fiscal period. But, for uses such as effective/expiration timestamps, simply storing the value in the fact is usually good enough.