I can't seem to find a single site (which would presumably mean a consistent methodology) that lists recent data for average|median use per day for both of them, but I've seen numbers saying people spend 33-50 min per day on Facebook, vs 90+ min per day on TikTok.*
I suspect the curated short video format is what really holds people's attention in a way that is different from "traditional social media".
*disclaimer: as reported by different sites, with different methodologies, and different reporting dates.
I've certainly seen friends and family compulsively scroll and obsessively check instagram and snapchat in a manner no different than what people are criticizing about tiktok. It seems like people witness their "their generation" using instagram/snapchat for hours on end; then they see the younger generation using tiktok for (the same number of) hours on end, and get the idea it's far more damaging.