My husband's student asked him to review a narrative she had written. She had written the sentence "5 hours later....." and when my husband questioned the use of the numeral "5" she advised him that her tutor says the rule for referring to a "time" number should always be written as the numeral.
My understanding is that if you are writing the actual time, it's acceptable (although not a rule), but for a number under ten, and a number starting a sentence, it should the the written word.
Does anyone know if there is such a rule as her tutor advised?
Edited to add: Her tutor had corrected her initial writing of "Five hours later..." to read "5 hours later..."