PSFTP does not support time-based file selection.
You can use scripting interface of WinSCP instead.
It supports time-constraints in file mask.
To download all week old (7 days old) files, use the following command:
get *<7D
See the guide for converting PSFTP script to WinSCP script.
For general introduction to WinSCP scripting see:
https://winscp.net/eng/docs/guide_automation
See also similar question WinSCP time based file download.
(I'm the author of WinSCP)