Returns the maximum size in bytes of the datetimes array represented in MF-JSON format.
For example "datetimes":["2019-08-06T18:35:48.021455+02:30","2019-08-06T18:45:18.476983+02:30"] will return 2 enclosing brackets + 1 comma + for each timestamptz 32 characters + 2 double quotes + 1 comma