20 years is a lot, but you're talking about completely shifting a market to something that literally doesn't exist yet. And that means creating infrastructure: it will take a lot to charge a semi. These are heavy vehicles designed to go 800 miles without significant down time.
So, yeah, maybe they could push harder. But it would be incredibly aggressive to make it 2030 -- for vehicles that don't exist and may not be available in sufficient numbers by then, at any price. Maybe call it 2035, but at that point we're talking about minor differences.
The main thing now is to make it clear that it's something they're going to do, so start planning to shift your fleet and don't come whining in 2030 when you say you can't do it in a measly 10 years. You had 20.
I don't necessarily think that it'll be done in that time and a 2040 deadline just makes that even less likely.
Not a perfect solution but sometimes perfect is the enemy of good.
When the political life cycle is 5 to 10 years nobody gives a shit about 2040, it's effectively "never"