先客户端验证，通过后再执行服务器端事件

function valueonClick() {

//alert("必须输入有效值");
            var nameValue = $("#Name").val();
            var time1 = $("#StartTime").val();
            var time2 = $("#EndTime").val();
            if (nameValue == "" && time1 == "" && time2 == "") {
                return true;
            }
            else if (nameValue == "" && (time1 == "" || time2 == "")) {
                alert("必须输入有效值！");
                return false;
            }
            else {
                var d1 = new Date(time1);
                var d2 = new Date(time2);

if (d1 > d2) {
                    alert("时间范围起始时间须小于结束时间！");
                    return false;
                }
                return true;
            }
        }

<asp:Button ID="Button2" runat="server" class="btn-default" Text="开始查询" OnClientClick="return valueonClick()" OnClick="Button2_Click1" />
   <input id="Button3" type="button" class="btn-default" value="清空" onclick="qingkong()" /></td>