When sending the THM message, the time on the board is synchronized with the given UNIX time stamp.  The standard VBA program, is sending this message automatic at the start and than every hour to the board to keep synchronized. When there is a RTC connected to the board, the time on the RTC is also updated. 

THMSendReceive@THM<UNIX time stamp> The UNIX time stamp is an unsigned long integer, representing the time since 1-1-1970 in milliseconds. 
Possible error messages coming from the board
%FAT-UNKCMD-BTSERIAL, Unknown command received