Can't backdate posts properly

Hi, I set up a news blog last week running Travelify theme. I have been trying to backdate posts to various recent dates but the edit function to change the time and date is only giving very limited dates to choose from (Jan 1, Feb 2, March 3, April 4, May 5, June 6 and so on). It has been doing this from the day I set it up. I have tried logging in with Chrome and Firefox. Any feedback will be much appreciated. I don’t want to start deactivating plugins yet in case there is a simple fix. Thanks.