Looks really great - I just installed it and am testing.
It appears to be possible to set the topic timer for a message - this actually seems like a more workable procedure to me. E.g. start a message to myself, set the timer and choose the category where it will go. But I’m not sure from the UI whether this will happen correctly. We’ll find out - I set one to be published in an hour! 
Update: the message did not convert into a topic in the specified category when published. So seems to me either the topic timer should be disabled/hidden from messages or support for it should be added so folks can do what I tried to do. Thanks!