We have the same issue. This error message shows up as a “critical issue” under the wordpress site health area so you should resolve it. Can’t you configure the plugin to use the same time zone that is set by the user under the wp general settings? why would you try to set your own timezone here? just use the wordpress general setting for this or at least give the admin the option so we can fix this.
Using WP 5.6.1, Ultimate Auction 4.0.8