"twice per day" is correct and usable in written English.
You can use it when you want to express that something happens twice, every day. For example: "I take my medication twice per day."
The intervention group received learning materials by SMS twice per day for 10 days.
injection twice per day for seven days.
Patients received either 2.5 mg DNase or placebo twice per day for 14 days.
Live-traps were left in place for three days and the traps checked twice per day.
Treatments were consumed twice per day for 12 weeks.
iOS users visit twice per day and read 12.5 stories.
This antiproliferative effect appears to be minimally increased at 75 mg/kg/day twice per day.
There were 10 animals per dose group and the doses were (1) control, Prang only, (2) low, 0.15 mg/kg of MPH twice per day increased to 2.5 mg/kg twice per day and (3) high, 1.5 mg/kg of MPH twice per day increased to 12.5 mg/kg twice per day.
Feces were siphoned out twice per day, dried and subsequently stored for further analysis.
At the time of presentation, she was being maintained on prednisolone acetate 1 %, twice per day.
The frequent defecation was gradually declining (about twice per day, Wexner's constipation score, 0).
