void SendMsg(char myMsg)
Passes SendMsg a signed 8-bit value.
void SendMsg(char * myMsg)
Passes SendMsg an unsigned 16-bit address to a signed 8-bit value.
Using the address (pointer) you can access that char, and others by their relative memory positions.
IMO best practice would be to make the original array big enough to hold the time stamp -- if you have to print just one string -- then strcat to that.
You might check but perhaps the twit thing looks for a newline or carriage return to determine end of message rather than timing out serial chars received or however it's supposed to "know" one bunch of print chars from the next -- you can fill the transmit buffer WAY faster than it sends chars out.