formula help,need to deduct 30 min if worked over 6 hours

i have this formula =D7+(C7>D7)-C7 which will allow me to total up hours worked over a 24 hour period weather it goes into the following day which is great.what i need is to add a formula to that so it will knock off 30 mins if i work over 6 hours in a day and dont knock off 30 mins if i work under 6 hours a day,your help will be much appreciated,thanks.
p.s. i've attached my time sheet.

Hi skagav,

Please correct / update your post title which describes the exact problem you are facing as the current title "formula needed" is not clear enough.
Also, please upload a sample file if possible. Thanks.

Regards,
DILIPandey

<click on below 'star' if this helps>