I would not wear the watch around the clock.
Have a look at this page of the user guide: https://help.apple.com/watch/#/apdcf2ff54e9
It says: "Remove Apple Watch periodically to allow your skin to breathe."
Skin sensitivities Some people may experience reactions to certain materials used in jewelry, watches, and other wearable items that are in prolonged contact with their skin. This can be due to allergies, environmental factors, extended exposure to irritants like soap, sweat, or other causes. You may be more likely to experience irritation from any wearable device if you have allergies or other sensitivities. If you have known skin sensitivities, please take special care when wearing Apple Watch. You may be more likely to experience irritation from Apple Watch if you wear it too tightly. Remove Apple Watch periodically to allow your skin to breathe. Keeping Apple Watch and the band clean and dry will reduce the possibility of skin irritation. If you experience redness, swelling, itchiness, or any other irritation or discomfort on your skin around, or beneath, your Apple Watch, please remove Apple Watch and consult your physician before resuming wear. Continued use, even after symptoms subside, may result in renewed or increased irritation.