What really helped me get this is the distinction between GMT and UTC. UTC is a universal method to describe time-instant. However, UTC is not a timezone. GMT

What really helped me get this is the distinction between GMT and UTC. UTC is a universal method to describe time-instant. However, UTC is not a timezone. GMT is a timezone, specifically, it is the timezone GMT+0. Representing a time-instant in GMT for universality is wrong, representing a date (i.e. the kind of thing humans use to denote appointments in their daily life) in UTC is also wrong. Use the construct that matches the domain.