From 100% to 99%? I don't know, maybe 5 or so minutes? Give or take a minute or two?
If your previous phones would take 20 mins to drop 1%, I'd imagine it wasn't calculating the battery % correctly. I mean if 20 min screen time is 1% drop, then *if it were accurate* then it should take 99 x 1% drops at 20 min screen time per 1% drop.
Quick maths:
99 x 20 mins = 2,000 minutes total screen time
2,000 minutes / 60 minutes = 33.33 hours screen on time
Yeah - no chance your previous phone had 33 hours screen on time. So it just wasn't calculating the initial 1% drop accurately. The S10 is probably calculating it correctly now.
With your S10 at 4 minutes for a 1% drop:
99 x 4 minutes = 396 minutes total screen time
396 minutes / 60 minutes = 6.6 hours screen on time
Much more reasonable screen on time.