When you create your account, Postcron automatically sets your Time Zone for you. However, if you want to change it so that the time of your posts matches that of another city or country, go to Your Account on the side menu where your profile picture is, and then on Settings.
Once there you will find the Time zone option and you can select whichever you prefer. Make sure you Save the changes!
Keep in mind that the time Postcron displays as Your Current Time will be according to the time zone you set up.