Convert datetimes to ISO 8601

[rskaliotis]

The existing code always interprets the datetime object as UTC, regardless of any actual timezone set on the object. This leads to incorrect values when using non-UTC timezones.

The API doc states: "Valid ISO-8601 formats are : yyyy-MM-dd'T'HH:mm:ss.SSSZ Example fromEnteredTime is '2024-03-29T00:00:00.000Z'."

It's ambiguous, but I believe this is saying valid ISO 8601 strings are ok, not just those ending in "Z". I've tested the API with a UTC offset (e.g. "2024-08-03T10:51:44.203150-04:00"), and it honors the time with the specified offset.