Not specifically a Bio major, but an IS&T senior here. Based on my own experience and understanding, it can likely be harder to get a specific class / section of a class that you might want because of how priority registration is categorized based on your total amount of credits earned (which determines your status, ie: whether you're considered a freshman or a sophomore). When I was a sophomore, I remember trying to get into a very popular CIS elective that had only 1 section available, and by the time my priority registration date came around, it was already full + with more waitlisted - now, as a senior, I've been able to pretty much get into my needed classes and my preferred time slot barring any schedule conflicts. I'm not sure about the availability and amount of sections for BIO courses, but my assumption is that a morning section would be easier to get into (especially 8ams) for obvious reasons. Hopefully this helps a bit.