Can I use the glass cups in an hotel room to drink?

You may use the cups for cold beverages, provided that the cups are clean and you don’t leave your liquid in the cups for 24 hours (or as soon as 6 minutes if it is a strong alcoholic beverage).

לענין שיעור כדי שיתננו על האור וירתיח – ראה הנסמן כאן: