Short answer
HubSpot's KB: Time zone is set manually from fixed options that don't update for daylight saving, so some zones are an hour off part of the year. IP time zone is set automatically from the contact's IP address and can be used for segmentation and reporting. Show both on the record so reps see them before calling.
1. The property
Contact properties in my demo portal: Time Zone is a dropdown select.
2. Use it
- Add Time zone to the calling view.
- Schedule marketing emails by recipient time zone where your tier allows.