Change is done each morning. If you are in space during that time, you will be warned ("Console message: Incoming Ion storm ..."). After this YOU NEED to restart game via launcher to synchronize your client and server market files. If you do not restart, then you will most likely be "kicked" right after you buy some commodities and undock from a station.
In SP if you want to have the dynamic economy functional, you will need to download the updates on a daily basis via the launcher.