In file included from C:\Program Files (x86)\Arduino\libraries\Time\DateStrings.cpp:11:0:
C:\Program Files (x86)\Arduino\libraries\Time\DateStrings.cpp:41:22: error: variable 'monthNames_P' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
PGM_P monthNames_P[] PROGMEM =
^
C:\Program Files (x86)\Arduino\libraries\Time\DateStrings.cpp:58:20: error: variable 'dayNames_P' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
PGM_P dayNames_P[] PROGMEM = { dayStr0,dayStr1,dayStr2,dayStr3,dayStr4,dayStr5,dayStr6,dayStr7};
^
C:\Program Files (x86)\Arduino\libraries\Time\DateStrings.cpp:59:24: error: variable 'dayShortNames_P' must be const in order to be put into read-only section by means of '__attribute__((progmem))'
char dayShortNames_P[] PROGMEM = "ErrSunMonTueWedThrFriSat";
^