In WebServer.ino the following line of code:

addFormNumericBox(reply, F("Message Delay"), F("messagedelay"), Settings.MessageDelay, 0, 10000);

defines a "message delay" that can be set in the "Tools->Advanced" config page to be used e.g when sending data to Thingspeak. However, to be able to send several values to Thingspeak a message delay of at least 15000 ms must be used. As can be seen above a maximum value if 10000 ms is currently allowed. Please change max value to 15000 ms as default.