Pick a file based on date after certain time.

Hi,
I have this requirements: this is SFTP(External system)-->PI-->FTP(within the network)

1. Schedule a job nightly, Monday thru Friday, to SFTP the delta file from XYZ company (some time after 5:00pm PST as that is the latest time XYZ would update their web site) connects to XYZ company FTP site.

2. Search for the current XYZ_delta*.xml file by date and if a new delta exists, select it and move it to a designated folder(within the network).

3. Rename the new file to a specific static name.

how can I approach this? is UNIX script is the solution? do i have anything in PI to achieve this? I'm using PI 7.11

Thanks.
Prema