While some recipes say it takes only 60-90 seconds to make mason jar whipped cream, I did not have that experience! Rather, my jar (starting with 1 cup of whipped cream) took about 8 minutes to whip completely and then a bit longer to get the texture to stiff peaks. I can't guarantee how long your jar will take, so my best advice is to listen! If the cream is still sloshing around in the jar, you've got awhile left to go. If it's getting quiet or heavy sounding, it's time to start checking in. Once the cream is "whipped" it can go from soft peaks to stiff peaks (and quickly to butter) very speedily, so that's the time when you'll want to open the jar up frequently to check on things.