You're asking and I'm answering . . .
"Fit, I usually work out in the afternoon, but recently I worked out in the morning and it was tough but my boyfriend says it's better to work out in the morning. I am thinking about changing it up, but do you know when the best time is to exercise?"
— Morning Molly
People always seem to want to know when the best time is to exercise, so to see my answer just read more.
My first inclination is to always say, "If it ain't broke, don't fix it." If you're happy with your current routine, and you're doing it, then there is no reason why you shouldn't keep working out in the afternoon. Now here's the good news: For optimal performance, you want your body temperature to be warm when you exercise (hence why I always stress "warming up") and body temperature is actually at its lowest in the morning, in contrast to late afternoon when body temperature reaches its peak. In fact it's been shown that exercise during these late-in-the-day hours produces better performance and more power — your boyfriend may want to check his facts.
That is not to say that if you currently work out in the morning that you should switch it up; you may just want to be sure to have an adequate warmup. Plus morning exercisers have been found to be more consistent in the long run.
So unless you're training for an event that is going to take place at a certain time of the day, the best time to work out, in my opinion, is the time that you'll actually do it.