The AI beats me to the Scandinavia chokepoint. I'm not sure it's possible, or if it is it's not worth it, to beat them to that chokepoint as I get there pretty fast and they are always there already. I beat them to East Russia, and Svalbard S. They beat me to South America and Australia, although I've considered trying out a new strategy where I beat them to South America (haven't, though). We usually get to the Canada point around the same time. Sometimes I will let them beat me there and take some Neutrals in Canada and then I'll clean them up afterward, and other times I beat them there and defend it. All depends on how things are going. In my last attempt, they beat me there and made some unexpected moves in Canada, which is why Canada was one of the later bonuses I grabbed, because I incorrectly anticipated their movements in there two turns in a row.
Taking bonuses along the way is a much better strategy than a "rush and defend chokepoints" one, because how are you going to hold the chokepoints if you don't have the income to support it? I feel like my strategy is kind of both...I get to the relevant chokepoints fast, but I take every bonus along the way there.
I feel like I have almost completely perfected my technique for beating the challenge, and 24 turns is probably pretty close to the lowest it's going to get using that method. I think 23, maybe even 22 is doable, but it would take some pretty ridiculous luck, and I had really good luck already to beat it in 24.
However, I think there might be a way to get a lower score trying out a different strategy. The two I'm thinking of are
1. Not abandoning in Svalbard S. and quickly spreading through and smashing bonuses in their Eurasia. This plan may involve an abandon in your East Russia or their South America, as you will probably need to restrict the AI in some location to make up for fighting them in 1 more.
2. Quickly pushing into their Canada from your South America and spreading quickly through the Americas.
I don't really have any motivation to try those out, though, as I already hold the record by a fair margin :). I was kind of hoping you or someone else was still working on beating it to give me some competition, and thus a reason to bother trying these out.