A Small Nit Question for Elapsed Time

[aesculus]

I have 5 variables (the amount of time the system is cooling, heating, aux heat, fan and off). These are supposed to be 1 minute long each but they can vary a bit, and when the system has to be restarted a minute or more can go by without data so the numbers can often not add up to the value of $timeFilter.

I would like to replace the Off value with a calculated value where the other 4 variables are subtracted from the $timeFilter duration and it becomes the new Off value.

Where and how would I do this? Right now in my query I get each variable from a Select and at bit of math:

sum(cooling)/60 AS "Cooling" FROM "HD21E10576_1_T" WHERE $timeFilter;

Likewise for Heating, Fan and Aux