Excel VBA to change time

[joemo2003]

anyone help?
Three cells, A, B, & C.
A is start time and date, let's say 6/5/2007 10:00am
B is the end time and date, let's say 6/5/2007 11:00am
C is the time interval minute, which is 60 in this case.

what i want is when i change the C to 70, A will change to 6/5/2007 9:55am and B will change to 6/5/2007 11:05am. and when I change C to 50, A & B will change to 6/5/2007 10:05am & 6/5/2007 10:55am.

any help will be great.
thanks

[joemo2003]

never mind, it is so easy.