How does a total of 40 hours per week affect the predicability of being there at the same time in a way that 35, 39, or 42 hours maximum per week could not?
my teams do the same thing, it works fine as long as there's some degree of predictability in the schedule. My team does a standard 40 hour work week but only 6 hours per day of required "core hours" used for pairing. The other two hours ar e flexible so the folks can adjust their schedules if they want to get in earlier in the morning and leave earlier.
9-4 you'll be in the office and ready to pair, and lunch for everyone is 12-1 regardless of when you got there; but you can come in at 7 and leave at 4 if you want, or get in at 9 and stay til 6 or work at home later if that works better.
you need that strictness of "pairing time starts now" otherwise you have people coming and going and needing breaks at all different times and it gets disruptive.
But the daily schedule is only dependent on the maximum numbers of hours to the extent that the hours have to fit within that weekly window. If we assume a five day work week, and the maximum weekly total is 35 instead of 40, then you may only have 5 core hours (or 6 core hours and one fewer flexible hour per day), but the predicability remains exactly the same. Changing the total hours per week does not mean having to throw out a schedule entirely.
I am afraid I still don't quite see what impact the total maximum hours for a week has to do with predictability of scheduling. What am I missing?