I have a list of date/time values which I plan to use text-to columns to
strip away the time.

Next, I need to convert these time values into half hour interval values but
don't know how to do this.

For example
Original Value Converted Value
23:16 23:00
09:56 09:30

So, you can see I'm converting the time to the last half hour that passed.
Can anyone suggest a formula or method to simplify this for me? Many thanks
in advance for any assistance.