Forget what you've been told about parking yourself cross-legged for twenty minutes and attempting for a "blank mind." That sentence alone was dreamed up by someone whose brain has only barely a few tabs running at once, ghost of yotei meditate.
The ADHD brain feeds on dopamine and novelty and and a stream of sensory information, so the opposite of those things (stillness, hush, repetition) when demanded of us, would in most people cause them to feel like something's wrong with them — like everyone else would — but also feel like a total failure. Which, again, does never really come from willpower — it comes from a mismatched approach. Two minutes is the target.
Don't reach for ten minutes.
Commit to just two minutes; which, in the first 30 seconds of which, you are going to lose it in some kind of dramatic way anyway; so with all due respect, the less runway you have when it first takes off, the less time it has to get away from you,and you can pull it back! Success is simply circling back —and this is your entire rep. When doing the rep for 50 occasions throughout two minutes,you would most certainly generate more focus muscle than someone who just sat quietly for twenty minutes on the floor —totally unaware of everything.
Movement works wonders; a walking practice, free-form dancing, even pacing your floor or the house; or anything physical at all while working on mindfulness... Whatever works! Consider pacing the house or the room with something to hold or touch and just pay attention to your breathing when it isn't a good situation at all —if anyone in the world were to watch your behavior! Surprisingly enough... "tidy up the kitchen" meditation (running water, hands busy and mind in its body) is frequently how the most present and intelligent minds genuinely find calm with meditation instead of a flawlessly posed, Instagram-worthy, meditative bliss pose.
Noise can be another rescue where complete quiet becomes hard to sit with in an ADHD brain. Put on your favorite meditation recordings, background tones, or even just the sound of the clocks ticking in your room and your brain will handle the rest by locking onto whatever thing it's listening to!
Timing of this meditation session within your daily schedule matters too... Should you have prescription medication that you take during the day then this is typically a much better time than right when you wake up, when your brain is far from switched on.