A quick way of getting rid of those is to go to the dataset viewer for that chart’s data and delete all the timestamp values. I don’t know if this chart’s dataset is dynamically changing, but I know that can be a real pain to have to delete each value one-by-one if the data is constantly changing. I would suggest using a scripting function like system.dataset.updateRow(), but there is an issue with saving “None” to the dataset, as the built-in dataset utilities in Ignition will coerce a “None” into a default value for that column’s data type (like 0 for an integer, or the current date/time for a date). This issue is fixed for 7.5.2.
In the meantime, suffice to say, an opaque container would work as a temporary solution.