This game has been designed at an introductory level. If, however, you would like students to have a reference point, direct them to view the half-past charts.
http://www.teachthis.com.au/products/view-resource/link/Half-Past-Wall-Charts/id/3712/
EXTENSIONS
Play a fast-paced class game of I Have... Who Has... time to the half hour.
http://www.teachthis.com.au/products/view-resource/link/I-Have-Who-Has-oClock-and-Half-Past-V1/id/4412/