Quoting My Widdle:" Whenever DD is awake I feel like I should constantly be interacting with her by talking to her or whatever ... [snip!] ... since she's been sleeping in it at night bc of her cold I want her upright. I get scared the vibrations will harm her somehow."
Honestly, I would take advantage of this stage while it lasts. Obviously you want to hold and talk to your baby throughout the day, but even the simplist things stimulate her at this stage so enjoy a little free time if she is happy to watch the lights, listen to music, etc. If she were bored or unhappy, she would fuss and cry. It's nice for her to learn a little independence and for you to get to do a few things done!
As for the vibration, all of our seats stopped after a certain amount of time passed. I don't know of anything harmful from it, but I just personally wouldn't want them always being vibrated (I don't have any logic to it but I would worry about sensory development).