I have nothing against hikers (would be hypocritical as someone who trail-runs) and blasting past people on a crowded path (or at all) is an idiot move. But on a single track trail people can come up on you really quick, 10km/h is a brisk jog so a 15km/h (4m/s) delta V isn't exactly fast.
My local trails are way quieter at 3pm (most people are in work and temperatures are still hot) than at 7am (pre-work dog walkers and exercisers). Saturday 7AM is literally the worse time in SoCal - big groups of riders and local running clubs all hit the trails Saturday morning. Guess it is varies by region but no matter the time I'd want to give other trail users the maximum oppertunity to know I was there so we can all be safe.
For the record I don't want to ride my bike fast on multi-use paths at any time of the day, not sure why you thought I did. If I ride fast it is on bike focussed routes (accessed via the multi-use trails).