Each person’s time diary in the ATUS data is made up of 1440 minutes, or 24 hours. Each time use episode or activity is coded based on a multi-level classification system that includes major activity categories (e.g., personal care), more detailed activity groupings (e.g., sleeping), and most detailed activities (e.g., sleeplessness).
Adding up time spent on all major activity categories will result in a total of 1440 minutes. Similarly, adding up all time spent on the most specific activity categories will result in a total of 1440 minutes. To reach 1440 minutes, however, you need to ensure that you have created time use variables that are collectively exhaustive. This means you have included every category of time use, whether you include an activity in its most specific form (e.g., sleeplessness) or in its most broad category (e.g., personal care). Your time use variables will also only add up to exactly 1440 minutes if they are mutually exclusive, meaning no activity is captured in more than one variable. If, for example, you created a variable that measured time spent on sleep, and another variable that measured time spent on personal care, there would be overlap between the two—sleep is an activity within the major category of Personal Care, and so time spent on sleep would be counted twice. The variables you’ve created so far do not seem to have a mutual exclusivity problem, but they are not collectively exhaustive (or will not be for all persons).
I highly recommend looking through the ACTIVITY variable on IPUMS ATUS, which allows you to see how all the activity categories are nested together. You can also visualize this structure when creating the custom time use variables you are using and expanding/collapsing the activities that you will include or exclude. When you create your own custom time use variable, you can select any level of specificity. But every activity must be included in order to add up to 1440 minutes.
The screenshot below is the activity selection menu from the ATUS custom time use variable builder tool. Here you can see the broad categories are Personal Care, Household Activities, Caring for and Helping Household Members, and so on. I’ve expanded the broad Personal Care category to show the second level categories: Sleeping, Grooming, Health-Related Self Care, Personal Activities, Personal Care Emergencies, and Personal Care, n.e.c. I’ve also expanded the Sleep category to show the most detailed categories:
You can also manually create a variable that captures time use on all other activities that you did not create variables for. In the programming language or software you are using, you would simply calculate 1440 - [time use variable 1] - [time use variable 2] = [time spent on all other activities]. This will only work if your time use variables are mutually exclusive, as described earlier.