To "write off" means to eliminate, typically used in finance or accounting. To "write off any time..." means to eliminate it, or don't count it. You act as though it did not happen. In this case, if there seem to be two records that are the same, one will be written off, or eliminated.

Benham's answer is definitely not correct, but it's hard to tell what your sentence means without a context. Is someone talking about a chart with different time slots in it?

I think "written off" here means "to be criticized"