First, regarding your flow - You can’t blend the output of 2 Things together that way. The two traffic things would never finish simultaneously, and whichever one finishes first will trigger the Math Thing to go ahead and start, so it will only have 1 value, it won’t wait for the other one. You can do it using variables and a short timer, but it's a more complex flow.
However, you say you are trying to add the two travel times in that flow. You don’t really need to do it that way - as I mentioned before you can add 10 to any travel time, the travel time is a number that can be added to. But you said in your previous post that you are looking for a way to add to minutes to an ETA time. That can’t easily be done, the ETA is a time in text format, its not a number, so adding to it won’t work right.
So what I was suggesting was to find some spot that is 10 minutes beyond your normal destination, and use it instead of your real work destination. For example, home to work is 20 minutes. (not counting the 10 you spend eating donuts). So you find a spot (location X) that is normally around a 10 minute drive from your work location. And it would have to be lined up so that if you asked a map program to show you the route from home to location X, the route would go right past your work location. Then you set your flow to give you the ETA time to get from home to location X. That will almost always be 10 minutes more than just going to work. (which would make up for the donut time)
Here’s another suggestion - use 2 flows. One flow, which you look at from home, would just give you the travel time to go to work, without eating donuts. Then when you get to the donut shop, run the other flow, which would give you the ETA to get from the donut shop to work. If the first flow showed a longer than normal time, then leave earlier. And if the second flow showed a longer time, then eat less donuts and get moving. You could even get fancy and use geofencing to automatically run the second flow when you arrive at the donut shop.
Or you could go out and buy a used Tardis. Then ETA’s and travel times become irrelevant!