The confirmation actually does already give a warning about exactly this. Here's what it says:
Please note that VDS adjustments can take extra time. We talk more about this in our Knowledgebase.
"We talk more about this in our Knowledgebase" is a bold red link there, though it doesn't show that way here in the forums.
Usability is always a delicate balance. We could make the warning bigger or bolder, or even make it a popup or extra checkbox that you need to click to get past, but that would de-emphasize other just-as-important information on the page, make the ordering process more cumbersome, and honestly wouldn't change much -- many customers click through on things without reading them. Since this particular operation isn't destructive, the usability trade-off versus the current warning may not make sense. With server deletions (highly destructive operations), it did make sense to prevent customers from continuing at all, which is why we require a special coupon code for those.
Everything on the confirmation page is very important, and it's a very concise page. I can't stress enough how important it is to read it.
expressing or covering much in few words; brief in form but comprehensive
1.Complete; including all or nearly all elements or aspects of something
My point here is that you don't say how much time it could take upfront. Your wording is "Please note that VDS adjustments can take extra time." and then you link to the KD thread. I find this interesting for these reason:
Your description is pretty vague. In reality, any upgrade takes "some extra time". That wording doesn't provide a strong distinction between the amount of time a VDS upgrade can take from any other upgrade (Which, as I had to learn the hard way, can significant). Then, there is the KD thread that you link to which is five paragraphs long. And in this thread you don't even start talking about how long the upgrade could take until the 4th paragraph. And that's fine, i guess. But this is where I get hung up. Out of all of the important information in that thread, the only part you chose to highlight on the confirmation page is in regards to the timeframe of the VDS upgrade (again, vaguely though). So, why then, if that's going to be the only part that you highlight, would you not be as concise as possible in regards to that? Why would you require me to go to a seperate thread and read through 4 paragraphs of information just to find out exactly what you mean by "Please note that VDS adjustments can take extra time."? Why not just say how long it could take in that one sentence...since that's the only part your are going to highlight?
Why not say, "Please note that VDS adjustments can take up to 'X' hours in some cases."...then link to the thread.
"Please note that VDS adjustments can take anywhere from 20mins to 'X' hours"...then link to the thread
Or several other one sentence combinations that would do a much better job of letting people know upfront exactly how long their upgrade could take.