If you think about it, some really complicated coding sessions require keeping the state of many pieces of the program in your mind simultaneously (see, e.g., this: http://heeris.id.au/2013/this-is-why-you-shouldnt-interrupt-... ), including code in many different files. This is actually more difficult cognitively than simply working on two separate simple and well-contained coding tasks simultaneously.
I haven't tried this for coding, but the equivalent would be not to start running a test until you know what the next function/method/commit you're going to make is. Even if you have to screw around looking for potential problems in your code, or potential places to refactor, don't run the tests until you know what that next thing is going to be.
Here's the actual Hemingway quote:
The best way is always to stop when you are going good and when you know what will happen next. If you do that every day when you are writing a novel you will never be stuck. That is the most valuable thing I can tell you so try to remember it.
You have created a problem for yourself that should not exist: do not task switch to Hacker News, task switch back to your text editor to re-read the code you just added or to work on the next part of the problem; or you could be working on two parts of the project at once and keep rapidly flipping back and forth between them. Your issue is not that you don't have the patience to wait for five seconds: it is that during those five seconds you are doing something useless instead of something else important.
In all seriousness, once you stop thinking of "patience" as "I need to be able to sit on my hands and wait" and instead think of it as "I now have the opportunity to do something else for the next period of time that I should try to make as productive as I can", I don't think ADHD is the problem anymore: the issue is making sure you always have a fun productive side task. You might find yourself accidentally doing things you realize later had low value for the time, but at least you got something done, right?
Put another way, you should embrace ADHD, not fight it: once you get into the habit of distracting yourself with just another task, the 5-10 seconds of compile time no longer matters, as you routinely switch to another task for five minutes every time you compile and it doesn't matter how long the compile took. You can do this with everything: I deal with delays in my web page e-mail client by having two or more clients open at the same time where I am working on two different search and reply tasks.