I had the problem with coreg (beta blocker and ace inhibitor). Coreg Cr is a single slow acting dose, and the same coreg dosage split to twice a day (morning and night) was more effective. Talk to your doctor.
I had a similar problem on Ramipril and was on 5mg a day. The Doctor re-prescribed the medication as 2.5mg to be taken twice daily. That did the trick for me.
An ACE inhibitor dilates vessels. A dilated vessel offers less resistance and as a result blood pressure in lowered. The timing of the effects may be of less help at intervals you describe. Also, dosage may inadequate.