But yeah, to make a big carbon impact, electric planes would definitely need fast turnaround.
Most charter flights are just to fly to somewhere nearby, drop someone off, fly somewhere else pick someone else up, repeat. Often the destination is some small airport that doesn't have jet fuel (most charter aircraft are turboprops) so you need enough fuel for the return leg or you make a 30min detour to somewhere that does.
The hops are often small but you often need to do many of them back to back without a ton of downtime in between and usage patterns tend to be not well distributed (not much happens on a Tuesday but on a Friday every rich banker is trying to charter a flight to their house on Nantucket or wherever). It's basically the same usage pattern as an uber vehicle will see only the vehicle itself is a proportionately larger cost so you can't as easily just have more of them to make up for charging time (like some electric bus fleets do).
Charter flights are one of the last things I can see being electrified unless battery swaps become a thing because the charging time directly hits profitability.
I think that's a very generous assumption. Typical small engine light aircraft cruise at 70-120 knots (80-140 mph). Wikipedia[1] suggests 211 mph as the current electric speed record (made in 2017). I doubt typical aircraft will be as optimised for speed as the one that holds the record. Increased speed causes exponentially increased aerodynamic drag, so if you want to increase range, slower speed [than your maximum speed] is the way to do it, not faster.
Or one option is that we normally don’t let li-ion batteries discharge completely to preserve battery life but that could still count toward your reserve with the right software.
Or I believe there are some existing one time use batteries that are way more entry dense than li-ion? Perhaps those could be part of the system just for emergency use and to meet reserve requirements.
Assuming 300 mph. The first case gives you an effective range of 75 to 150 miles. Second case gives you 375 to 450 miles range. That's 3 to 5 times more effective range.
Go on google earth and start drawing 450 mile radius circles around population centers. Yeah that.
Bonus: Eviation is claiming an estimate of 650 miles range with their yet to fly Alice.
The two big advantages with electric flight are fuel costs and maintenance costs. For electric the fuel cost is a third to a quarter lower. And electric motors should have a much longer service life and lower maintenance needs than turbo props.