ClickUp reads and provides dates in various formats during imports and exports. 

Normal

• Day, date, time, timezone offset

• English formatting

• Date fields without specific times are set to 4 am in the local timezone of the person setting the field. 
  Example: May 30, 2019, PST would be Monday, May 30th, 2019, 4:00:00 am–07:00

ISO (International Standard)

• Year, month, day, (T) time

• Date numbers separated by a hyphen ("-")

• Time numbers separated by a colon (":")

• Date numbers less than 10 are preceded by a zero
  Example: May 30, 2019 would be 2019-05-30T11:00:00.000Z

POSIX

• The number of milliseconds that have elapsed since January 1, 1970. 

• This format is the easiest for machines to read and perform calculations and comparisons with

• Also known as Unix time, Unix epoch, or Unix timestamp.

• Amazing converting tool: https://www.epochconverter.com/.
  Example: May 30, 2019 would be 1559178061000