When you are using Sheetgo smart schedule to run your workflows automatically you need to specify which timezone the workflow will use as its own. If you have many workflows you can opt to set one specific timezone for all the workflows in your account.

To do that you need to go to your Account page, click on your profile picture/icon, and select Manage account.

From there go to User Preferences and select the timezone that you are in.

And that's it, now all your workflows that already have a smart schedule or any future workflow that you create will all follow the timezone that you've specified.

If you need your workflows to run on different timezones you can do this individually in each workflow. On the workspace, click on the trigger icon and open Trigger Settings.

Select the unique timezone for that particular workflow and click on Save.

If you need to change the global timezone of your account or any particular workflow you can do this freely following the same steps you did to set the timezones.