Alarm

I am working on a "live" whiteboard. I have to keep track of times and in one column I have a critical time. Is there any way of setting an alarm in a cell so that the time shown in it starts flashing 30 minutes or so before the time is reached?

I am new to using Excel and to this forum.

Thanks to anyone who can tell me how or if this is done.

Chip Pearson has code for blinking text here: http://www.cpearson.com/excel/BlinkingText.aspx