First off, if the coffee tastes good, you don’t need to worry about hitting a certain time just to do it. But if you do want to:

I don’t have this kind of machine, but I know that most folks say that single baskets are inherently difficult to work with, and you should just a double instead. That’s not to say you shouldn’t use the single, but maybe look for some single-basket tutorials that might have specific advice?

https://www.youtube.com/watch?v=y0XariiJiHk

https://www.youtube.com/watch?v=3OnH2Woluck

In terms of slowing down your shots, other than grinding finer, you can also increase your dose within a given basket.

Also, if your GCP is stock, then it might be worth doing the overpressure valve mod. By default, those machines have a really high pump pressure, and replacing OPV spring with a 9 bar or lower one is a very common mod for the GCP.

I’ve never used either device, but it sounds like you’re grinding a hair too coarse. Are you able to go a bit finer?

And re steaming, unfortunately the biggest drawback to cheaper espresso machines is a subpar steam wand, I’ve never had luck steaming milk on a budget oriented machine. They typically use a thermoblock to steam water from the boiler, which simply doesn’t give you a consistent steam output.

Single baskets are tricky to get right, did you try with the double basket (with a slightly coarser grind) and the same ratio? The taste is the most important thing in the end, so don’t fuss too much on exact timing.

Steaming milk requires a lot of trying and patience, focus on getting the tip at the right height and slowly you will learn when the air is mixing correctly with the milk and when to change position or stop.

And follow the tip about the actual zero of your grinder!