Does DateEquals compares both date and time?

Hello.

I think "DateEquals" is only comparing dates.
If you want to include time in the comparison, I think you need to use "DateLessThan", "DateLessThanEquals", "DateGreaterThan", and "DateGreaterThanEquals".
https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements_condition_operators.html#Conditions_Date

For example, if you create a policy like the one below, it will be possible to allow EC2 operations from UTC 2024-05-21 to 2024-06-01 23:59.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": "ec2:*",
            "Resource": "*",
            "Condition": {
                "DateGreaterThan": {"aws:CurrentTime": "2024-05-21T00:00:00Z"},
                "DateLessThan": {"aws:CurrentTime": "2024-06-01T23:59:59Z"}
            }
        }
    ]
}

The word "Date" in operators like "DateEquals" or "DateLessThanEquals" can be confusing. The "date" values being compared are full timestamps that contain both the date and time, technically represented as the number of seconds since the "epoch", which is a certain reference time in the past, such as Jan 1st ,1970.

Your conclusion is right, though: if you want to allow or deny an entire 24-hour day, you have to evaluate it as the range of timestamps between the second that starts the day (DateGreaterThanEquals) and the second that starts the next day (DateLessThan), or in other words, d ≤ x < d+1. Still to be clear, it isn't a matter of "working around" anything but simply that you are wanting to allow/deny a range of seconds instead of a single moment in time, and the timestamps you're comparing against always represent a single moment in time.