I took pepcid ac 20mg yesterday around 1pm. i took another one at 9pm. would it be safe to take another one the next day around 10am?

Yes. This dosing: is fine BUT are you certain that you are treating the right thing? If you need that much Pepcid AC to treat your symptoms you might want to be evaluated by a health care professional to be certain you aren't mistaken about your diagnosis and actually need different care or medications.

Proper evaluation...: Usual recommendation is 2 x in 24 hrs. If one is having so much Acid Indigestion/ heartburn to require recurrent use of Pepcid AC, it might be a good idea to make a face to face appointment with a Gastroenterologist for proper evaluation & management