Short answer
HubSpot's KB: Super Admins and individual users can set out-of-office periods in the user's time zone. While out of office, availability is Away and the user isn't eligible for automatic assignment. The user record shows the period's start and end.
1. Availability
Availability management in my demo portal.

2. Workflows
HubSpot also documents an Is out of office property for workflows to reassign tickets.