25; twenty-five
The number 25; used for counting, ages, quantities, etc.
I will be 25 years old this year.
1 a.m.
Only when written ２５
Colloquial time expression using the 24+ hour system; 25時 means 1 a.m. the next day. Restricted to the ２５ spelling.
クラスには二十五人の生徒がいます。
There are 25 students in the class.
Last night I stayed up until 1 a.m.
Arabic numeral spelling, very common in horizontal writing and for the time sense.
Abbreviated kanji numeral; rarely used in modern writing.
The ordinary numeral 二十五, “twenty-five.” The “1 a.m.” sense comes from extended 24-hour notation, in which 25:00 denotes 1 a.m. on the following calendar day.