I think I see what you are trying to do. You have a model that groups by step with a sum of time per step. You want 2 fields one where the time per step (for example) is >0 and <10 and the second is >=10 and <=100. What I would do is create 2 models: one to aggregate steps for the first condition (>0 and <10) and one to aggregate steps for the second condition (>=10 and <=100). In the second model add a Model UI Formula field with a Model Lookup function to pull in the other value.