ADHD experts tell us that for us ADHD'ers, there are two kinds of time - Now and Not Now. This is partly because our brains crave efficiency in the immediate moment. Why would we waste time planning and pre-thinking about something that is not easily reachable right now, right? :) For example, we might think "I need to prep for that project" while we're playing a video game. We'll immediately jump to the next question: "Do I need to do that right now?" But unless the project is due in the next 5 minutes or so, we probably won't engage with it. The deadline likely has to become "Now" for it to get our full attention.
Of course, we can see how this could cause problems! The power bill that's not due "now" isn't a problem until the lights get cut off. (Dang! I was sure i had another day!) The non-urgent email that you need to respond to isn't a problem until the irritated client asks you about it a week or two later. Logically, we can agree that delaying undesirable tasks isn't good for us in the long run, but seeing this in the moment requires high executive functioning.
Executive functioning is the ability to manage our minds like an executive would manage a business. An executive manager would ask tough questions from a perspective that can see the whole picture of the company’s situation. They might consider what departments are functioning well and have plenty of resources and what departments need more development or resources so that the company functions better as a whole. An executive considers the performance of each department day-to-day and can put the brakes on or press the gas pedal when necessary.
Try this: picture a little mental-manager inside your brain. (Mine looks like Mr. Monopoly.) The manager is in charge of directing your brain's activity in problematic scenarios by accelerating or braking. The manager can re-direct attention when needed, even if it means you have to take a break first. The manager can make sure you're focusing on what is actually important to you rather than on the easiest thing to do in the moment. The manager knows what to do to shut down over-thinking, self-doubt, self-blame, regret, etc. (Hint: If you get stuck in these, try taking a walk, punching a pillow, eating something, reading a book, screaming into a cushion, doing a puzzle, working out, or doing whatever shuts this down for you.)
Sometimes it's easiest to summon our mental manager by picturing ourselves from across the room. In a loving and supportive way, ask yourself what an encouraging manager observing you might say that you need to be doing in this moment. Remember that the manager is a part of YOU, and there's no need for shame or blame or regret to motivate you. You can lovingly re-direct yourself over to the most important, wisest, best thing to focus on at the time.
This may all sound impossible. And yes, it would be impossible (and unhealthy) to try to use this every moment of your life. These strategies are best thought of as tools in your toolbox. They are resources to keep in your back pocket until they're needed in a stressful or unfocused moment. You'll probably find that you actually use them more often than you thought you would. I use them several times a day. They don't always fix the problem entirely, but they generally make it easier to get through the problem. They build confidence as they are practiced and mastered over time. So go ahead and start them now. Don't wait until not now.