Epoch option?

I am trying to figure out a way of getting data from the meters not using ISO 8601, as it is a pain to work with in the HTTP Client I am using due to the ":" and ".". It says in the API Reference that EPOCH in seconds is also accepted, but I have never gotten that to work. Is there an example that could be provided?

My current string that works with ISO 8601, but not EPOCH.

curl "https://api.streamlabswater.com/v1/locations/<location>/readings/water-usage?startTime={2019-10-17T11:00:00.000Z}&perPage=1" -H "Authorization: Bearer <API_KEY>"