Because of my schedule, the only times I can find for the gym are either VERY early in the morning... like 4-5 a.m., or later at night, say 8:30-10:00. I"ll be the first to admit that I'm terrible about getting into an "early up" routine, but I've always thought that this was the most productive time of day to workout.

So help me out with this decision. Is it better or more productive to workout in the morning as opposed to shortly before bed... do you need to be consistent with workout times, or would rotating back and forth between times not make a difference????

Thanks in advance for any advice with this. (it will be mainly cardio work with some light weightlifting)

The Most Productive time is whenever you can give your Best Effort!

Some People swear by The Morning being better.....Some Say it really doesnt matter....IF it does matter it is probably just a small difference.

if you dont have the energy to have as good a workout in the morning then do it in the evening.

I used to Workout every night at 10pm and and it great for me.

The best time is when you can make it to the gym!
Don't worry whether it's morning or night time. IF there is any difference in effectivness, it is so small as to be totally insignificant.
I work out 7 days per week and I have tried a variety of schedules. Lo and behold! They all work just as well for me. So, don't worry about the timing. Just get to the gym anytime you can and do your best.