Honestly I've found the opposite to be true lately. I just booked a trip last month and Friday was way more expensive than leaving Saturday morning. The airlines know everyone wants to start their weekend getaways. Tbh I think they've caught on and adjusted their prices. It feels like the old travel tips don't really work anymore. You gotta check multiple days and times to find the actual deal.
My last flight booking was a mess. I checked prices for a Friday, saw they were high, and smugly waited until Tuesday because some article said that was the cheap day. The price doubled. I ended up paying more for a Wednesday red-eye than the original Friday flight. I guess my big brain move was just giving the airline extra money.