1.
four days
A duration of four days.
四日 uses native Japanese counting and means both "four days" (duration) and "the 4th" (date).
USAGE:
- Duration: 四日かかる (takes four days)
- Date: 四日に届く (arrives on the 4th)
- 四日間: four-day period (adds 〜間 for explicit duration)
DAYS 1-10 (SPECIAL READINGS):
NOTE:
Days 11-31 use regular 十一日 pattern, except 十四日, 二十日, 二十四日.