GOOD screening takes time. "Hey, look, he's got a bunch of review and is whitelisted, good to go!" - that is not exactly thorough screening. About whitelists...most guys for them, and a few will even blatantly pester girls for a referral. If a girl doesn't comply, she risks a retaliatory bad review or backchannel.
There are tons of whitelisted guys I'd never see, and some of them are blacklisted, too. Not all girls have the same standards - a client who is perfectly acceptable to one girl may be a terror for me, depending on what he is into and what she will allow. All I take a whitelist for, is that a guy showed up, he paid, he left without causing her undue harm and wasn't unreasonable (by HER standards, not mine). I screen for a lot more - I don't want to see a guy who will be a complete asshole, a complete pig, who is demeaning, who will ask to pee on me or tie me up, who will try to remove the condom, who will be rough, who will work me like a team of oxen, who won't respect my time, who can't be pushed out the door, and so many more things. But, some girls will tolerate any or all of that, and I know some guys who have really bad reputations and whitelists as well.
Also, reviews can be fake. Happens all the time. Even if they're real, how is it screening? It gives you HIS perspective of the time. Maybe she didn't have such a great time. Maybe he shorted her. Of course, he wouldn't put that in a review.
With that said, I sometimes do see guys same-day. However, YMMV. It all depends on his demeanor when contacting me, and how easily I can verify him in that time frame.