The regular season ends on Sunday October 1, and the first wild-card game takes plays on Tuesday, October 3. That will be the American League game, with the National League one - hopefully including your Arizona Diamondbacks - occurring the following day, Wednesday, October 4.
Both leagues have an off-day between the wild-card and the start of their Division Series. This year, there’s no split dates: both division series in the league will take place on the same days. The ALDS starts Oct 6, and the NLDS - again, hopefully including your Arizona Diamondbacks - is Oct 7.