Of course, if you have no heart damage or symptoms, then you shouldn't need to be on beta blockers for more than a few months.
I look up to you having an exorcise bike "indoors". Snow, Freezing temp.s, Wind, for this past week and expected for the next few days. I did have the idea of building a stand for my mountain bike so I can ride it indoors like an exorcise bike, but I'm not allowed to make such noise. :-(
I asked the very same question last year, with the exception of the medication, I'm taking carvedilol which is an Alpha "and" Beta blocker. I assumed my heart would over work without the medication and it wouldn't work hard enough with the medication.
For the very reason Ed mentions, it's probably best to take it before so that you don't over do it.
Well, I think you are expected to take the medication every morning and the idea is for it to protect your heart, from over working. I would take it as soon as you wake up each morning, whether you are going to exercise or not.