In your ActiveCampaign account you will typically have it set to your local time zone. This allows you to set campaigns to run at at time you are familiar with. Equally this could apply to deals, tasks, automations. Any feature that you are using.
In the background however, ActiveCampaign will record the events at a different time. We have seen both UTC (which is universal coordinated time) and also Chicago time (which is where ActiveCampaign are headquartered) in the connector resources.
What this means for you, is that you may want to convert these timestamps to your local timezone (especially since Looker Studio Date Range Control is in the local timezone).
To do this you will need to convert them with a formula.
We are in New Zealand which is (UTC+12) so would create a dimension using DATETIME_ADD(ldate, INTERVAL, 12 HOUR) as we are 12 hours ahead of UTC.