Really too many factors to name, your asking an almost imposible question!... HOWEVER, I will do my best to shed a little light on the situation.
In most lakes in where the visibility is bad do to water clarity, you can have some very good DAY bites... where just after sun up till about 9am can be great.. In clear body of water, this is not as frequent. In clear bodys of water you are better off fishing the evening bite. From sundown till 3-4 hours after?
Other things that will change this will be weather. Weather can greatly change when crappies feed. Also, if there is any kind of larvae hatch. Food will change when crappies feed also.
To answer your question the easiest, the best time to go is when you can!