Joseph Rézeau

I'm afraid moodle 1.8 is very old stuff. Version 1.9 has been available for quite some time now and I strongly advise you to upgrade to 1.9 (and to the 1.9 version of Questionnaire, which is much better than the previous version).
All the best,
Joseph

On the Modules and plugins, on the Questionnaire page, click on Download latest version or Download for Moodle 1.9 (they're exactly the same).
To check that you've got the latest version, on the Download in text format page, this is what you should see (options to include choice text).
Joseph

You could use/adapt the function by Charles W. Reace, Jr. here.

If you have the start and the end dates in unix timestamp format, then instead of

$start = strtotime('2009-08-4 00:00:00');
$end = strtotime('2009-08-5 00:00:00');

just put the unix timestamps:

$start = strtotime('1249340400');
$end = strtotime('1249426800');

Please note that you may have to add one second to the end date. And if you are only interested in days, you'll have to modify the timeDiff() function accordingly.

Joseph

Nitin,
Do you want a formula to calculate the difference between two Unix timestamp dates ... in days? in days and hours ? etc. Please be more specific.
Joseph

Ivan,
If you could post here a mockup screenshot showing exactly where you would like the date and time to appear in your theme I might help you do it.
Joseph