Yes that's how it works .. the ( not unreasonable ) assumption is that you pick the car up with you arrive and drop it off before you catch the flight home as that's what almost everyone would want .. and the price they quote reflects this and I guess the T&Cs just ( somewhat confusingly ) confirm how rental companies charge 'days' as 24h periods from pickup

More exotic itineraries on here might make that a less reasonable assumption.. but that's what the custom trip builder is for and you can change the rental period easily enough with that