Wa Alaykum Assalaam,
Regarding the approval of threads, the time taken does vary.
Some threads are very straightforward - the source is cited and easily recognised to be reliable. Or the purpose of the thread is seen to be constructive and of some benefit. These are approved quite quickly.
Other threads require more of a judgement. The moderator checking the thread may be unsure about the source, or might be concerned that the thread may lead to more harm than good. In this case, the thread takes longer to approve because the moderator who checked it might wait for someone else's opinion, or they might wish to have some time to think it over.
Threads that are unapproved for a long time are likely to be those that we are not comfortable to approve, although occasionally it could be that they've been missed. We try to provide reasons for this to the original poster where possible.