It appears that this feature was added to the GUI but never entirely implemented. For now I have added the functionality, but its not very user friendly yet. To download the latest DEVELOPMENT release that has this feature go to http://www.bleeblap.com/CamStudio/weeklybuilds.php

Important: At this point the defaults don't make much sense, but thats part of a much bigger issue with how it saves user settings. You will need to change the default text color and size to make it appear.

To customize the timestamp you can now use any of the following:

%a

Abbreviated weekday name

%A

Full weekday name

%b

Abbreviated month name

%B

Full month name

%c

Date and time representation appropriate for locale

%d

Day of month as decimal number (01 – 31)

%H

Hour in 24-hour format (00 – 23)

%I

Hour in 12-hour format (01 – 12)

%j

Day of year as decimal number (001 – 366)

%m

Month as decimal number (01 – 12)

%M

Minute as decimal number (00 – 59)

%p

Current locale's A.M./P.M. indicator for 12-hour clock

%S

Second as decimal number (00 – 59)

%U

Week of year as decimal number, with Sunday as first day of week (00 – 53)

%w

Weekday as decimal number (0 – 6; Sunday is 0)

%W

Week of year as decimal number, with Monday as first day of week (00 – 53)

%x

Date representation for current locale

%X

Time representation for current locale

%y

Year without century, as decimal number (00 – 99)

%Y

Year with century, as decimal number

%z, %Z

Either the time-zone name or time zone abbreviation, depending on registry settings; no characters if time zone is unknown

%%

Percent sign

So to accomplish what you want you should probably use %H:%M:%S

Let me know if it works for you.