Is there a limit?
We have a Babybjorn bouncer, so its more hammock like and lays back. His head isn't forward like in a car seat, and neither is his back.
Baby is 8 weeks old. He won't be put down on floor more than 5 mins at a time. I try to get him to nap in pram if possible, and otherwise he just wants to be held, walked around or in sling
However its so hot where we are (30 degrees approx), that holding him longer than the time it takes to feed, or int he sling he is just getting super sweaty and all worked up and hot. the bouncer is cooler and calms him down to snooze.
He is probably in it about 3-4 hours per day at the moment. Thats split into maybe 2 1hr naps, and then whilst we eat, shower etc. He naps for another 1 hr ish in pram, and the rest of the time, about 10hrs a day he is being held or in sling still with odd 5-10 mins attempts on playmat.