UBB.threads doesn't have a "20 last posts" feature, but maybe one of these will serve:
1) Go to Active Topics in the navigation bar and select Active Posts, and you'll get a list of posts made in the last 7 days. Near the top of that page, over on the right hand side, is a Past 24 hours
link; bookmark that and you'll have a quick way to check for recent posts.
2) You can see a list of your own posts at My Stuff > Posts.