Rewatching What-If and while the first time I thought they did a decent job matching the timeline with Fury's Big Week, having recently rewatched those movies and reread the tie-in comic, it's actually messy.
Things start out fine. The episode begins on Monday and shows Tony, Fury, and Natasha at the diner. Perfectly matching Monday, May 30th, 2011. However, after that, it's like they skip a day placing events like Coulson finding Thor's hammer and Thor at the crash site that evening on Tuesday when they should be Wednesday. Sure, you could chalk stuff up to "alternate timeline" but things like when Thor arrives on Earth or Ross going after Banner shouldn't really be different from the Sacred Timeline.