I would like to have a formula where I can input a date and time from
one time zone (HKT, GMT, etc...) and have the conversion time be my
local time (Central Time Zone [CDT]).

Suppose an HKT date/time is in A1 as an Excel "date & time" value, for example:
Tuesday, July 29 @ 10:00:00 AM
using the custom format
Dddd, Mmmm dd ""@"" h:mm:ss AM/PM"

In B1, put the formula
=A1-13/24
and using the same format get
Monday, July 28 @ 9:00:00 PM

Explanation:

Referring to
http://www.timeanddate.com/library/a...ons/timezones/
the difference between HKT and CDT is 13 hours; that is 13/24 days.

Since daylight savings time isn't universal, the formula should change over the year. For example, U.S. Central Time uses DST but Hong Kong does not. To be thorough, you would have to keep track of time standards in the places of interest to you.

Hope this helps.