Scheduled rebuilds of indexes

I am on a Mac, OS X, running Acrobat Pro XI.

I have a number of saved indexes as pdx files

I add files to the indexed folders on a daily basis and as a result have to regularly rebuild the indexes.

I would like to be able to run a scheduled rebuild during the night.

I understand that I need to create a bpdx file in order to do this.

I have been into preferences and have permitted the construction of bpdx files

I cannot see how to save an index as a bpdx folder or how to create a bdx file.

I have looked at the online forum in relation to this and there is no obvious answer to the question and a number of people appear to have had the same issue.