The best time should be around June and July. It really depends on the quantity you are buying. If you would buy large quantity, and shipped from Asia then you need at least a month for the delivery. Before the delivery, you need around 45 days for the production if your products are in significant quantity. The early summer should be for the presentation time, and the purchase decision time. Hope my two cents help.
We are trading company in Hong Kong, so we deal with customers in the U.S often. We do exports. We understand how this works. If you need some help, please do not hesitate to contact me.