I have been pleased to learn that I can add / subtract hours in org-table to shift time zones.  I am making tables of  lunar/solar parameters relevant to tides.  Org-table is a convenient way to enter data in a tabular format that can be printed via LaTeX.  So each year, for several time zones, I enter these times by hand.  

It's very, very easy, I have learned, to collect all of these times (at most, maybe 12 per month) for UTC, and add or subtract to generate a column of times for a new time zone.  Very Slick!

Except that when I add, for example. 09:00 to 23:33, I guess it is pretty obvious what is going to happen: it would be the same day, but at 32:33 !!

I have tripped up on trying to test for whether the sum is greater than or equal to 24:00, and then doing something interesting with it.  It's actually pretty easy to go through all the months and find the exceptions, and make manual changes.  But, as I usually have done, I would rather spend a few hours coming up with some programmatic method for making this work automatically!  

The other problem is the change of the day.  I suppose I could use 0, 1, 2... for Sunday, Monday, Tuesday...  (I am living in the United States). 

Has someone solved this problem?

Thank you,

Alan Davis