You will likely need to utilize some Windows API calls via local external function declarations, such as GetFileTime and FindFirstFileW. If your app is based on the PowerBuilder Foundation Class (PFC) framework, the File Service objects (pfc_n_cst_filesrv & pfc_n_cst_filesrvunicode contain both the WinAPI function declarations and code to use them.
If you are not using the PFC, you could obtain the PFC libraries and inspect the code in these objects (both of the non-visual objects I have mentioned reside in the pfcapsrv.pbl. The PFC libraries are available to anyone on GitHub.
Also visit Roland Smith's TopWizProgramming web site. It contains free sample code addressing a wide variety of topics. Download & check out his Filesys app.