Look at Android GetTimeStamp local file handling

FDateTime GetTimeStamp(const TCHAR* Filename, bool AllowLocal)
{
#if LOG_ANDROID_FILE_MANIFEST
FPlatformMisc::LowLevelOutputDebugStringf(TEXT("FAndroidPlatformFile::GetTimeStamp('%s')"), Filename);
#endif
FString LocalPath;
FString AssetPath;
PathToAndroidPaths(LocalPath, AssetPath, Filename, AllowLocal);

if (IsLocal(LocalPath))
{

#if !USE_UTIME
FDateTime Result;
if ( NonUFSManifest.GetFileTimeStamp(AssetPath,Result) )
{
return Result;
}

if ( UFSManifest.GetFileTimeStamp( AssetPath, Result ) )
{
return Result;
}

#if LOG_ANDROID_FILE_MANIFEST
FPlatformMisc::LowLevelOutputDebugStringf(TEXT("Failed to find time stamp in NonUFSManifest for file '%s'"), Filename);
#endif

// pak file outside of obb may not be in manifest so check if it exists
if (AssetPath.EndsWith(".pak"))
{
// return local file access timestamp (if exists)
return GetAccessTimeStamp(Filename, true);
}
#endif
struct stat FileInfo;
if (stat(TCHAR_TO_UTF8(*LocalPath), &FileInfo) == -1)
{
return FDateTime::MinValue();
}
// convert _stat time to FDateTime
FTimespan TimeSinceEpoch(0, 0, FileInfo.st_mtime);
return AndroidEpoch + TimeSinceEpoch;
}
else if (IsResource(AssetPath))
{
FTimespan TimeSinceEpoch(0, 0, ZipResource.GetEntryModTime(AssetPath));
return AndroidEpoch + TimeSinceEpoch;
}
else
{
// No TimeStamp for assets, so just return a default timespan for now.
return FDateTime::MinValue();
}
}