how to increment a variable's value which is of type time

Question

Hi,

I want to know how to increment a variable's value which is of type DateTime by half an hour.

i.e if var is a variable of type double we can increment it as

for(double var=9.30;var<=16.30;var+=0.30)

similarly if var is of type time then how can I increment that by half an hour.

plz help

thanks