This is a drug that is used infrequently in the usa - more in australia.
Is that where you are? It has a short half life: 1 1/2 hours but is prescribed as a once daily med which i find frankly confusing. If your BP is rising 10-12 hours after a dose, it would make sense to me to take it twice a day. If your late day BP is elevated, you may need a larger am dose than the evening dose.