Once you enable SD card recording, it continues on the card independently without the app connected. Multiple cameras can all be recording to their cards at the same time.
In order to retrieve the video from the cards and save locally, you must play it back live and record it live in the app while playing it back. Unfortunately, this can only be one one camera at a time and only in real time.
The other option is to remove the card from the camera and transfer the videos from card to computer like you would any other file.
There is a #roadmap topic that you can vote for being able to directly download the files without removing the card. You can vote for it here: Direct access to SD card with download ability. Be sure the click the VOTE button at the top.
Three is also a #roadmap topic for being able to download time lapse video while on a non-local network here: Timelapse download on non- local network.