As long as you have a good one (a Large one), not too long at all provided you have good manual dexterity with traditional media
A traditional tablet is more accurate and affords a far better posture option than a display tablet, the problem with smaller traditional tablets is the "velocity" that comes from having a small drawing surface (both Small and Medium tablets) covering a display that is far larger.
You probably got a small tablet, most people don't understand the consequences of that decision-even fairly experienced artists-and they purchase the small ones thinking they're being "thrifty". There's even a highly rated video with hundreds of thousands of views someone posted in this thread where a person (who is not a line artist themselves) claims that the tablet "Doesn't Matter®". They're full of shit and should be ashamed of themselves, I've heard that statement regurgitated a lot and nothing could be further from the truth. This is not to say that good work can't be done on smaller tablets, however if you value your time or your health even a little there is absolutely no reason to go the cheap route.
>This problem doe not exist on pen displays
Not necessarily true. Pen displays have a problem called "parallax" which means that there is a small but consequential discrepancy between where your stylus is on the screen and how it's being interpreted by your tablet and computer. Screenless tablets, to that end, are objectively more "accurate". However the problem with cursor velocity is significant. On a modern small tablet you can expect something like a 1:3 movement distance to drawing distance relation between the tablet and a typical display. It is very important to close that gap as tightly as possible, to the point where no expense should be spared to achieve that.
>are stands worth it
I wouldn't think so, it just seems like something that'd get in the way.
>draw at an angle
No unfortunately you can't draw in that manner with a Wacom stylus iirc, I do agree that drawing like that is more comfortable and it's one reason I still very much enjoy drawing in pencil.