Keep in mind that 18 months or two years is usually the minimum amount of time to wait for a promotion, unless you've had a discussion about shortening that deadline even before you're hired. According to Ian Siegel, CEO of ZipRecruiter, early career employees should aim for promotion every three years. The most likely time to receive a promotion is in your third year with a company. Visier found that promotions dropped significantly after 10 years with the company.
You can choose to wait until your annual review to show a year's progress and accomplishments, or you can choose to ask at the opportunity time when a position opens or led a successful team project. Wait until you've reached an important goal and received public feedback on your work to start this conversation.