Vanee 90H-V-ECM ERV defrost

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I'm having a hard time to understand how defrost works in these units
As you can see in the attached image the manual say that if its warmer than -5 it runs 7/40 and -5 to -15 its 7/25 etc

What does it means if I run the ERV lets say for 10 min  and its -2 outside ? Is it going to run defrost for 7 min and then 3 min normal ? And what is going to happen if I will run for 10 min more lets say 15 min later ? since its still in the 40 of 7/40 is it going to run without defrost ?

I mean if I run the ERV all the time I can understand that in 7/40 it will run 7 min defrost and then 40 min normal and then again 7 min defrost and then again 40 min normal, but whats going on with ERV if I don't run it all the time ?