Let me know if you get a chance to plan a trip and I will try and help you out. It is a great experience.
The best advice is to look at the tides, and plan a trip when the tides are good. Normally the tides are pretty good towards the end of summer/fall. Earlier in the summer the tides can be less predictable, i.e. the prevailing winds can keep the water out, while in the late summer/fall the prevailing winds often bring extra water in. I use a tide log, and the best bet would be to check the tides ahead and plan a trip when you have tides that are going to be from 7.7 to 8.3 for the majority of your visit. Now these tides are for the Beaufort/HHI area and are uncorrected at the Savannah River Mouth. Tides for other parts of the coast would be different, and I do not know what constitutes a good tide in the Charleston area (the tides there are lower than they are in my area). Hope this helps.