Why does it take minutes for a new post to be successfully uploaded after submitting it?
Minutes? Only takes seconds in my years of experience here.
That is a particularly concerning aspect, for in the past if it takes too long things timeout and the post will be lost.
Timeouts can be frustrating, I agree. If it makes you anxious, consider copying the content of your post before hitting the submit button. That's a simple process change that will eliminate this particular concern of yours (since that content can easily be pasted into a new post in case of failure).
Is there a reason for this or is there something I can do to correct this?
[This post was accepted almost immediately, just to prove me wrong but the post prior took what seemed like more than a minute.]
Well, given that it doesn't happen all the time, and you just acknowledged yourself that it just submitted immediately, I'm going to say no.
There are too many complexities here. This is how it works, and you'll need to be okay with that.
It depends on the site software, the server running it, the software on that server and what kind of hardware they use, your local internet connection, your own computers speed, and countless other factors that are (speaking from experience) nearly impossible to hunt down and resolve (tools like Fiddler help if you have access and ownership of every single connection point, but we won't be able to do anything about those findings here).
EDIT: I have experienced this past week or two some strange hourglassing where it appears the post wasn't submitted, but if I open a new tab and load the page fresh the post appears and I have confirmation that it worked even though my previous tab continues to hourglass. I'm not sure why this occurs, but it's too sporadic for me to worry too much right now.