In file included from C:\Users\Vishesh94\Documents\Arduino\libraries\Time\DateStrings.cpp:11:0:
C:\Users\Vishesh94\Documents\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:\Users\Vishesh94\Documents\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:\Users\Vishesh94\Documents\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";
^
Error compiling.
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In file included from C:\Users\Vishesh94\Documents\Arduino\libraries\Time\DateStrings.cpp:11:0:
C:\Users\Vishesh94\Documents\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 =
Update your third-party time library to a more recent version instead of using an outdated library with a new Arduino IDE!
The compiler is telling you that the arrays must be const in order to be stored in PROGMEM. It is not rocket science to edit the file it is complaining about, and add const to the offending line.
If you don't understand how/where, again it is not rocket science to search this forum for that message. The step-by-step instructions have been posted more than once.