Updates about your work can take up to two hours to be shared with your network and updates about your education can take up to 24 hours to be shared with your network. Work anniversary notifications are sent within that month. In other words, simply acclimating to your new job will fill your plate, so save LinkedIn for later. You immediately jump to LinkedIn for your new job ad, only to realize that you don't know how to create your post.
This is probably an unsatisfactory answer for those wondering when to update LinkedIn with a new job, but the truth is that when you share your work update it will be personal to you, your position and your company. Wait until you have a better understanding of what the job is actually like before expressing it in your own words on LinkedIn. Updating your LinkedIn profile to reflect your new position isn't as simple as introducing your new job. You can post your new job on LinkedIn using the same method you used to update your position before.