There is a bug in the implementation of timezones in all current versions of the Infoplus API where times are indicated as GMT/UTC, despite their values actually being shifted to be US Central time. For example, a value returned by the Infoplus API of 2020-07-04T16:00:00.000Z should actually be: 2020-07-04T21:00:00.000Z (it is off by the US-Central timezone offset, which is 5 hours during daylight saving time, 6 hours during standard time).
To avoid this behavior, and get proper timezone behavior from the Infoplus API, you can include the HTTP header: X-Infoplus-Proper-Timezone-Behavior with a value of 1 in your API requests.
This is a huge issue for us as we have SLA to meet for our client. Our Client SLA is if the order is in InfoPlus before 2:00 p.m. EST then we must ship the order. If not then we have missed the SLA.