Twice a day.
"Day to day" should not be hyphenated when used as an adverbial phrase, such as in "She manages her tasks day to day." However, when used as an adjective before a noun, it is often hyphenated as in "day-to-day operations." The hyphenation clarifies that the words work together as a single descriptor.
Every day.
you should laugh every day it is good for you
every day
twice a day every day
every day
Every other day or every day
Every other day should be enough
Every day.
Every day is common hygiene.
once a day
every day