Setting ONE timezone

We are using this plugin for our client Wegmans. All of their stores are on the East coast. The countdown timer is 5 hours off of what it should be and I cannot find anyway to correct that. I would assume that the timer would be based on the timezone set under WP Settings>General, but apparently that is not the case. I read something about server time. I did see that there was an option to set it to User time, but the time never changed. Can someone help me with this? Client is overly anxious. Thank you

https://wordpress.org/plugins/uji-countdown/