They are quite close in meaning. "Day by day" refers to process and the passage of time, such as the famous dictum of Emile Coué: "Day by day, in every way, I get better and better". Other examples:...
No it is not. It can be but it changes every year. Last year it was on my birthday and its on the 19th. So it can br but its not every year!Hope this helps.
Day-to-day. It's a hyphenated word.
Parp.
There are 244 days between Anzac Day (April 25th) to Christmas Day (December 25th).