In what format should the date and time parameter (departure_time/arrival_time) be specified in the Google Get directions API?

Question

API

Hello.
What is the correct way to specify the value for the date and time parameter in json format? How to convert date/time/time zone to acceptable json format (integer in seconds since midnight, January 1, 1970 UTC)?
Attached parameter description:
departure_time (same for arrival_time)

Specifies the desired time of departure/arrival. You can specify the time as an integer in seconds since midnight, January 1, 1970 UTC. If a departure_time later than 9999-12-31T23:59:59.999999999Z is specified, the API will fall back the departure_time to 9999-12-31T23:59:59.999999999Z. alternatively, you can specify a value of now, which sets the departure time to the current time (correct to the nearest second)
https://developers.google.com/maps/documentation/d...