If they're slouching over Uncomfortavle they aren't ready. But if they look like they aren't struggling it should be fine for short periods at a time. Mostly Four months is good. My baby is 3 months and can kinda sit for a while but I won't leave him in it long.

Every babies different! Use your own judgement mommy! ☺️

my baby just made 3months and I pit her in it

I never got one cause they were too expensive lol. But if I would've gotten one I would've used it at around 4-4.5 months. That's when my kids sat up well with support.