Record count is not part of the external file metadata. Don't have access to DIS at the moment but if you don't specifically set a max row count, you'll be fine. The record count in your screen shot is just for that dialog, will not be registered in metadata.
Do you mean that the file name will contain a time stamp? If so, the most common is to solve this by using a macro variable in the External File physical path, and build some logic to resolve it to an appropriate value at execution time.
Data never sleeps