It depends on your category.
In busy categories, Linkedin can be like talking to a friend at a concert. You are screaming (posting 7 days a week), but they hear a whisper (low engagement). In those cases, it could take a couple of quarters. No different from any new marketing channel.
In sleepier spaces, the results can be immediate. For instance, I have a client who was able to grow her following 50% in a month and was able to get inbound leads immediately, and that’s from only 3 posts a week.