it is correct to say 'starting from the first day next month, study hard' but again i was marked wrong! i am a native speaker of english.
What is 일일 here?
First day, i think? 일--1(according to the Sino Korean system), 일---day(also Sino Korean and used when counting days)
"Study hard starting the first of next month." is also wrong. I flagged it.
please also accept "first" instead of "1st"