The reason you see the timestamp when you export your data from Paxata is because, in the project, that column represented Paxata DateTime values. This has some benefits, namely:
1) You can perform temporal sorting (sort ascending or descending chronologically)
2) You get extra filtering options available for datetime values (5 available charts)
3) You can use temporal expressions to tinker with the dates -- dateadd, datediff, month, year, etc.
NOW, you have identified the downside of exporting the data in this format -- it includes all those greyed out characters that represent hours, minutes, seconds, timezones (Z) etc. So in order to get a clean export, as a last step, you may consider converting your datetime columns into text by using the computed column dateformat expression:
1) Trigger a computed column step by clicking on the compute tool on the left-hand toolbar (calculator icon):
2) Create a new column and give it a name. (Hint: if you want to override the existing column, name your column the same thing as the column you are overriding.) Then click the calculator to the left of the expression bar to select the dateformat expression. This function requires 2 arguments: 1. the column whose format you would like to alter, and 2. what you want the syntax of the new date to be. Hereis an article that explains this a bit more in-depth.
Then, when you publish the data from your project to the library and export it from the platform, you will see the dates in a much friendlier format. My only advice is that you do this as a last step so that you can preserve the extra datetime functionality as long as possible.