I think the point of that was partial transfiguration was a low hanging fruit that could be done fairly easily, but only if you had the right mindset. Other than having to hold timelessness in his head, it's not any harder than regular transfiguration.

Come to think of it, you're right.

I'd been approaching it from the "hero must struggle for several episodes to get awesome powers" angle, but Eliezer was obviously writing it to demonstrate the opposite.

(Although Harry being able to hold timelessness in his head with half an hour of trying is still Marty Stu-ish.)