About thirty minutes. According to the entry, this form is often used in Kansai dialects and may be considered archaic or dialectal in standard Japanese.
会議は半時間で終わる予定です。
The meeting is scheduled to finish in half an hour.
（関西弁）ええやん、半時間だけ休憩しよか？
(Kansai dialect) Sounds good — shall we take a half-hour break?