Sister is unforgiving with computer time.
I am one more step away from throwing myself into a wall with this. Okay, my five year old sister and I are both gamers, and where I'm living now, we have two computers. The purpose of having two was to easily divide our cycle of usage between each other, so we wouldn't get roped into an automatic argument. At least that's what I THOUGHT would happen. The main problem lies between the computers themselves; one, which is my stepfather's, has sixteen processors and can run games at insane speed. The other is fairly older and is pretty sluggish when it comes to stuff like Minecraft or GTA IV. We have our turn cycle worked out like this; when my stepdad isn't using the computer, I go to his and my sister goes to the other computer and we both enjoy ourselves. Then there comes a point where she's bored of the game she's playing. I know what you're thinking; when she's done, she grabs a snack and sits down to watch SpongeBob or something, right? WRONG. Instead, I hear her tiny feet running into the bedroom asking "can I have a turn? Can I have a turn?" This is the core of the problem; if there's TWO computers in the house and I'm using one of them, it should be enough that the second computer's available. Nevertheless, no matter what I do she talks over me and argues until I decide she won't shut up until I give up my turn. I know I shouldn't be so easily aggravated with a child but it's kind of hard when whenever I say "I'm still using my turn" she talks over my words and chants "I want a turn I want a turn I want a turn". If I DON'T give in, she runs to my stepfather and then I'm forced off. This is utter BS. Because of this I rarely have time to talk to my friends or family, I rarely have time to work on a game I'm developing, and I have only seconds before I can finish a video for my Youtube channel. I'm sick of this happening and I want to nip this in the bud so bad but I can't get anywhere if my sister keeps arguing with me and talking over me. I've tried everything in every book and nothing works. Somebody PLEASE tell me what I need to do.
What about me? Can *I* have a turn? (LOL, sorry, couldn't resist)
It sounds to me as if this is but a symptom of a far more complex problem that you and your little step-sister are caught in the middle of. I get the strong impression that step-dad is biased because  little blister is his child,  it's his computer,  he (I'm betting) feels guilty over having subjected his daughter to a broken home and is foolishly being lax with her to make it up to her,  not being technically savvy, he doesn't appreciate how important and non-child-friendly your 'work' is,  he'd rather she pestered you than him, *and*  she's the baby of the family. Hence she gets special treatment.
At roughly just one year away from her psychological blueprint becoming finalised, that little girl vitally needs to learn her place in the pack and to have a bit respect for others, with a view to knowing how to make places for herself without antagonising people when it comes to the bigger packs (different arenas in society), and for so many reasons, not least of which is as follows:
Nobody's going to automatically give her special dispensation and privileges out in the real world. More likely, what with her being taught repeatedly that pushing, making a coercive pest of herself and seeking out and appealing to whichever (hopefully biased) higher power is a way to force the other person to have to relent - what she'll end up with is an adult life full of crushed expectations and constant fists in her face, metaphorically-speaking (or these days, quite possibly literally!). In other words, she is being encouraged to sit on yours and her father's chest and thereby get ideas above her station and that is *not* good parenting (specifically, it's known as Permissive, and results in spoiled rotters).
(What about your mum, where's *she* in all of this?)
However, her *reason* for being a pest is obviously a mixture between the fact she (obviously, at only 5) lacks your greater attention-span, wants attention from you, her impressive big brother, and confirmation that her dad is still wrapped around her little finger as a learned form of reassurance that he still loves her and isn't going to be going anywhere.
The thing is, though, that, your favourite computer being stepdad's, he *could*, if he wanted, not be letting you use it at all. That he is is at least something and shows he thinks he *is* being fair. So I think his main trouble is his being incapable of understanding exactly what it is you do on there. Have you never invited him to watch? Maybe if he knew the full extent of what you do and thereby more fully the situation, he'd instate rules that are proportionately and age-appropriately fairer?
Going deeper, this could also be in the mix as a reason: "Because of this I rarely have time to talk to my...family". Are his own expectations ("Dadda Number Two!") disappointingly not getting met? I ask that not only because of the behaviour he's teaching his nipper but also because I note you don't mention having had a sit-down talk with him about it.... plus the fact that most men, even though loath to admit it, always dream of having a son. So maybe, even without consciously realising it, he's using the opportunity of his pester-power kiddie to loosen a few of your ties to your family im the hope that you'll pay more attention to him?
On the practical side, there are lots of solutions for taking a straight approach or boxing really clever, but first I need to know, How old are you and how old is your stepdad (AND WHERE'S YOUR MUM)?
Tell me what you've so far tried?
PS: Spongebob's sh*t; Grimm, Billy & Mandy rule! ;-p