I read this in an article and really liked it: The best time of day to exercise is when you'll do it!
There are many schools of thought about this subject, and from what I've seen, personally, it depends on the person. For example, I cannot exercise in the morning before eating or I will get extremely ill. Also, I find that if I exercise too late in the evening I can't go to sleep well. So, if your schedule allows it, try several times and see what works best for you.
Now, to address the feeling crappy during dinner - is it physiological (does your body feel bad? nausea, etc) or psychological? As long as you're eating a good healthy meal, you're not "messing up" or canceling out the good you've done in your workout. Keep up the good work, and let us know how it goes!