If you request the data in CSV format you will get get a date/time format as seen in my screenshot below.
My example query looks like the following.
The docs for querying metrics can be found below with an example for the CSV format at the bottom.
Unfortunately I can't see a way to request the time in a date/time format when getting a response in json.
If you tied the application name to the synthetic with tags, as far as I can tell that isn't possible without making another request to get the details on the synthetic in question. Using the returned synthetic ID you can query the synthetic API to get all details including tags.
Below is an example
No! currently there is no way you can get that response change from api. You can use a post processor script.
Also check this solution if helps