WELCOME ABOARD, Arctic Wolf!
One of the things you can do with Commander is change the number of days between patrols. I usually leave it set for 'Random', but when I start a career at the beginning of the war I run a 'practice' patrol on August 1, then set it for 18, which lets my first real patrol start on August 19, which is when fourteen u-boats were historically sent to wait for...? (they weren't told)