i take atenolol which is a beta blocker too (although its a little different). when i first started taking it, i could feel when it was time to take the next dose, because my hr would increase. now i'm on a higher dose and i don't feel that anymore. perhaps you need to be on a higher dose. but your situation seems a littler different from mine, so i can't adequately say; only give my experience. i don't have high blood pressure (low bp actually), so that might mean something different.
I would think the time-response you describe is very unusual, especially for your relatively low dose of Metoprolol. I have taken as much as 100 mg twice a day, time approximate, morning and night, about 12 hours apart. I have also changed to 50 mg twice a day, just started that lower dose this past Sunday.
I take it to lower my HR, and it helps, but I never see anything lower than 70 BPM. It could be lower when I'm asleep, but I have no way of knowing as I'm not on a recording monitor.
I think your reactions may be driven my your emotional expectations... just a guess.
Also right around the time for my next dose this morning I was having second thoughts about taking it and went about 15 minutes past the time i been taking and began to have chest pains. I decided to take it and went to the ER just to be sure the pain subsided my EKG was beautiful the doctor said. I'm wondering was that a symptom that started to happen because I waited to long without taking my next dose. I've read stopping this med abruptly can be dangerous.