You are correct that the Archive_AutoArchiveFileSize is the tuning paramter you are likely interested in. Note that the units of this parameter is MB. If the parameter is currently set to the value of "0", on shift the new primary archive file will be created with the same size as the current primary archive. In your situation, it sounds like setting this to 256 would probably give you what you are looking for. The parameter takes effect on each shift, so a restart of piarchss is not necessary.
As for scheduled archive shifts, this is currently an enhancement request on our uservoice, I will add the link below. If this is something you are interested, please vote for the idea and submit a quick use case to help us with prioritization.
Hope this helps,
This video details how to configure archives & enable automatic archive creation. In the LiveLibrary, we also have documentation on the Automatic archive creation tuning parameters. As you will note from the documentation, when autoarchivefilesize is set to 0, it generates a new primary archive file that is the same size as the current primary archive file.
Let me know if you have questions on either of these.