The fact that the automation cannot trigger based on the item’s designated date and time is ridiculous, and goes against all logic as to having the automation trigger in the first place.
For example, I’m trying to have a notification go out to the item’s assignee at the date and time of an appointment field, in order to remind the person responsible for that appointment to update the status of the appointment. I should be able to choose the date and time of the appointment, and then how many minutes, hours, days etc after that date and time the notification is sent.
You can combine the solution of Bas de Bruin
with 1 or 2 number columns - numbers as hours and minutes and create multiple automations “when date arrives” + “number is” and you will have the outcome