Master data is imported from the source system at regular intervals. You have defined a time interval for each import.
Let's assume you are on the Master data import page for a specific company under Settings > Data > Import - Master data. You have defined a time interval of 15 minutes for an import. If the import is carried out while you are on the page, for example, you must refresh the page with Reload imports in the ribbon in order to obtain the current results.
See also