꾸준히 means more like “regularly” So there is a long period and you have studied for a long time and every day or almost You can say 저는 일년 동안 꾸준히 공부했어요. (I’ve regularly studied for a year) If I want to say i worked all day Then i would say “ 오늘 하루 종일 “계속” 일했어 “ 계속 : continuously 계속하다 : keep doing something So the first one is more like 계속 situation The other one is more like 꾸준히 situation FYI: 쉬지도 않고 : without a break 자지도 않고 : without sleeping