A. Unfortunately the answer is no.
For most funds, as long as you submit your "buy" or "sell" order to your broker before 4pm, your order will be executed at 4pm, exceptions do exist.
For example, out of the total 16,000 or so mutual funds, several hundreds of Vanguard's funds have 3pm as the "cutoff" order execution time. This means if you submit your buy or sell order after 3pm today, your order will be executed based on the next trading day's fund price.
This is another lesson for many people - read the fine prints before you invest.