Slot collection_date does not require value to indicate timezone

[eecavanna]

The https://microbiomedata.github.io/nmdc-schema/collection_date/ slot is defined like this:

nmdc-schema/src/schema/mixs.yaml

Lines 2825 to 2840 in bdf58f0

	collection_date:
	annotations:
	expected_value:
	tag: expected_value
	value: date and time
	description: 'The time of sampling, either as an instance (single point in time) or interval. In case no exact time is available, the date/time can be right truncated i.e. all of these are valid times: 2008-01-23T19:23:10+00:00; 2008-01-23T19:23:10; 2008-01-23; 2008-01; 2008; Except: 2008-01; 2008 all are ISO8601 compliant'
	title: collection date
	examples:
	- value: 2018-05-11T10:00:00+01:00; 2018-05-11
	from_schema: http://w3id.org/mixs/terms
	aliases:
	- collection date
	is_a: environment field
	slot_uri: MIXS:0000011
	range: TimestampValue
	multivalued: false

If the value is 2018-05-11, I don't know which timezone that is in. The same real world instant of time might be late on 2018-05-11 in California while being early on 2018-05-12 in New York.

I am afraid consumers will find the date values in this field to be ambiguous.

Are the absences of both (a) a requirement that the value include an indication of its timezone(s), and (b) a statement saying how schema-driven software will interpret a date string (e.g. whether it will assume it is in UTC), intentional?