Dialectal (Kansai) and obsolete in standard Japanese. In modern standard Japanese, use 三十分 (さんじゅっぷん) or 半時間 is not used.
Grandma in Osaka sometimes says 'Wait half an hour.'
Compound of 半 (half) and 時間 (time/hour). The reading はんじかん follows regular rendaku. The word is now dialectal/obsolete in standard Japanese.