In American English, through can be used to refer to time. It means ‘up to and including’.
- The office is open from nine through six.
- The park is open from March through June. (= March, April, May and June)
In British English, through is not used in this way. Instead, British people use structures like ‘until the end of’ or ‘to…inclusive’.
- The park is open from March until the end of June. OR The park is open from March to June inclusive.