What Time Span For Prescription Of 2 Tablets Per Day Indicate?

I take several meds a day. I know to take clonidine every 8 hours (rx. calls for 3 per day). Glyburide/metformin 5/500 at 3 per day basically at meals; Others I take twice per day, morning and evening.Does prescriptions that say take 2 per day mean two at a once or 12 hours apart (Lisinopril 20/25 and potassium 200. When is the best time to take 1per day (metroprolol, presvastatin)