You can expect Sildalis to last for approximately 36 hours. You must be sexually aroused for this ED treatment to work. Though the drug will stay in the body for 36 hours, you will not have an erection for that period. Sildalis takes about 30 to 60 minutes to take effect. Doctors recommend taking this medicine on an empty stomach. They also advise avoiding alcohol and grapefruits while taking this medicine.