How can I define my work week in 30 minutes steps?

Hi developers,

I have the following problem: A customer wants to define his work week with e. g. start time: 8:30am and can only chose between full hours. Is it possible to define lower iterations (e. g. 30 minutes steps)?

We defined it in /_layouts/regionalsetng.aspx.

Can anybody help me?

Best regards,

Björn