All you need to do is change the counter amounts. Right now the code(in the pictures) has it going to 360. If you have the room speed at the default of 30, it will change in 12 seconds. If you have it set to 60(which I like better, as it is much smoother), it is only 6 seconds.
There is a built-in variable for the room speed. You can use it. So if you want 10 seconds worth of steps, multiply 10 by the room speed variable. If you want 1 minute, multiply 60 twice(preferably in the same line). This way, if you change the room speed later, you don't have to come back and change this code at all. It is a lesson you should learn, basing calculations on constants and variables so that if you have to make a change, it is only in the one place. For example, that array for the bullet speed. If you want to change it, you only change it there, and any other thing that needs it can access it. That is a lot of the point of controller objects.
Side Note: I'm going to be getting back into GMStudio I'm thinking. I DO like Unity and 3d for projects, but I'm finding out that things take longer to get done, including coding(not just the graphics). One limitation of GMStudio that I didn't like was how with GML code, you declare variables in the create event, but then have to remember exactly how you named them when you use them in other events. You don't have that problem in Unity as the script events are all on the same page, and you have intellisense for your own variables too. GMStudio does intellisense, but only for built-in stuff, and resource names, and constants, but not for declared variables. The 3rd party Parakeet IDE changes that, and a lot more. I'm doing the 7 day trial of it and would likely buy it and use it. It fixes my one biggest complaint with GML. If you are interested in what I'm doing, I'll share.