Only 20 minutes ... luxury ! Mine normally takes about 3 hours.
You can initiate a manual check at anytime by starting Content Manager, opening the File menu and selecting Quick Database Repair or Extended Database Repair.
This however, will not necessarily stop Trainz from performing this function by itself and whenever it is most inconvenient to you. This can happen if the computer is switched off while the Trainz database is still open. It can take a little while for Trainz to close the database after the program has been terminated.