Excel 2007 : Maintenance table

Hi guys again,
In the past I had nice experience with this forum, for most of my question I got answer, thanks guys.
I need help with excel maintenance table, when we change something on the machine I will put date or working hours (from hours counter), next cell will contain periods between two changes (date and hours).
Could you give me instruction how look table which give me next point of change (date or hours, which is achieved first) and show me one message about that(it this possible).

Simple example is attached.

Thanks a lot in advance.