AFAIK, WBZ only has one Reporters Roundup from 12:30 - 1 p.m. Mon. through Fri.
As to their traffic and weather reverting to the 3s and 10s on the weekends, I agree with the previous posters that it doesn't make a lot of sense to me. It could be that they will be phasing in the T&W together on the weekends similar to the phase in during the week over the past 3 weeks or so.
Or it could be that they will leave it this way on the weekends to provide time for the expanded sports reports at :15 & :45. Sports reports have definitely been downsized considerably during the weekdays now that they have T&W together on the 3s. In fact, it wouldn't surprise me if they go with sports updates from "The Sports Hub" during the week. What this means for their current sports reporters is anyone's guess.