I actually don't get what the drama over this is all about. This was announced early on, it was one of the first bits of information we get about the game, it's not a recent change or anything.
Anyway, I have a feeling the idea of the system is being misinterpreted. This is essentially the same mechanic as the one used in TW2. You meditate and pick which potions you wish to consume (the amount of potions you can take is limited by toxicity, as it always has been, so you can't take all the potions you've created, probably 2-3, Witcher 2 allowed for 4 not very toxic potions at most). The difference is that instead of the effect being activated immediately, you can choose when the potions start to work. This is done in order to avoid situations like the boss fight at the end of chapter 2, where you knew what you were going to face once you enter the mist, you took your potions and then... you had 15-20 minutes of body switching and by the time the actual boss fight started, the effects of your potions had worn off.
The reason why this is a better system than drinking potions on the fly is that if you enter a cave expecting to find vampires but it turns out that you're actually facing a giant, then that 'Black Blood' potion that makes your blood poisonous is now wasted and useless, and it takes up toxicity that could have been used for a potion that gives you a bigger hp pool so that you can take a hit from the massive enemy. It means you'd better make sure you *know* what you're getting yourself into.
As for drinking the potion on Monday and activating it on Sunday, I assume that there's a longer timer on them that gives you a certain period of time when you can use the effect, like it was in TW1, but the actual effect lasts only a few minutes, like it did in TW2. Yes, the whole metabolism allowing you to activate an effect when you need it is bullshit in terms of lore, since Geralt clearly can't control that in the books (as shown in the part right before the striga fight in 'The Last Wish' book, where Geralt has to be careful not to show Ostrit his superhuman speed caused by a potion), but it allows the system we had in TW2, which required more research and preparation before a fight, to work better when the battle you're preparing for might not happen soon enough after you've consumed your potions.
A good example would be the Leshen fight. You don't want to waste the potion effect while destroying the totems, you need when you actually face the Leshen. The new system allows you to do just that. Anyway, I hope that clears things up a bit.