I believe its not the observer pattern in this case,
If the action of collecting files is just on time interval, then i don't see any design pattern here,
if the action is based on factor like the server is intelligent to say that the files have been changed and so the client can access it:
1. Client can 'poll' the server after an interval, if server responds a "yes" client can then initiate file transfer session.
Modified version of polling:
2. Client sends a poll, but server does not respond immediately but after a specified time interval, if files are changed, it sends a "yes" or a "no" - requires thread running at the server.
3. Client sends a poll, server discards the request if nothing has changed. Client gets a time out after a long interval and re-sends a poll. if something has changed, server returns a "yes".
There was a name for this special type of polling, it does not come to mind right now...
from client every 5 or 10 mins, it sends request to the server.
Then server sends a list of files.
This part is 'collection'.
After 'collection', 'export' need to be done [consolidate all files that have been collected during the 'collection' period].