Subtracting time from a date in Excel

I have a cell in column 3 that contains a datetime: 5/1开发者_如何学C2/2011 8:13AM. I'm looking to subtract x hours from this time.

So far, I have this:

=A3-TIME(8,0,0)

It's not working. How should the formula be written?

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Removed the space between 13 and AM.

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Use DateAdd instead of voodoo/rolling your own.