Is ther any service to sort the files in a folder based on Last modified timestamp ???
Sort files in a folder? what does that mean? Are you saying, you need a sorted list of file names? There are no-built in services for this. You will have to write a java service.
Yes . Sort the files in a folder based on timestamp rather than the file name .
Is ther any built in services which could be useful to create a flow service ?
Once you have a list of files and their timestamps, possibly in a document list, you may find the package at http://www.wmusers.com/software/uploads/710ReList.zip useful for sorting by date.