Hey @TheCosmicBob! Thank you for taking the time to share your feedback regarding our new Discussions forums here in the Forum Feedback section. I sincerely apologise that we were unable to reply to your thread until now, and acknowledge the points you raised. I'll do my best now to address each point; please let me know if I can help further with any of them, or if you have any additional feedback to share.
Idle time too short
A session time-out will occur after you have been inactive for a while, but should definitely not be as rapid as ten minutes or less. Can you please advise me of whether this is a persistent issue you are still encountering at the moment? If so, which browser are you using, and what version number is it updated to please? I raised an issue previously regarding frequent log outs / timeouts so I'll need to check if this is reoccurring.
Linear or threaded replies
As @Strayngel has indicated, there is a mix of threaded/non-threaded replies on Discussions. Replies to a specific post are expandable from that post itself, as to make it easier to view these if they have been posted much later in the thread, but they are also available later in the thread as individual posts for anyone wanting to read the full discussion chronologically. I have a conversation open with the developers already on this subject, and the suggestions from several users to either go fully threaded or unthreaded. Thank you for indicating that you would prefer threaded replies; I'll add your comments to that conversation! 
Preference for pagination over infinite scroll
As @EggKnobble kindly advised you (thank you!), you can enable pagination from your own forum browsing settings. You can also select there the number of posts / threads you want to view per page, up to a maximum of 20. I hope that this has made your experience of browsing Discussions more enjoyable in the past few months!
@Strayngel - Can you please clarify what you are trying to achieve r.e. sorting posts by "recent"? Are you trying to invert the display of posts within a thread to show newest first? Or something slightly different? Additional information will allow me to try and help you, and advise accurately as to whether there is an issue or not. Thanks!