Hi, you need at least 400 job experience points to get promoted to CEO. This is equivalent to working for 400/5 = 80 days which is roughly 80/5 = 16 months. So, it usually takes more than 1 year to become CEO.
You get maximum 5 job experience points every working day if you arrive on time + finish the job.
You can check your job experience points by first going to the work building & then tap/click info button on top right of the screen.