5.12 seconds, UR shitting me...
appx 5 sec any hot outlet, 3 to 4 sec cold, with the exception of the kitchen cold side.
probably look at servicing/replacing the cold mixer, or looking to see if there's any restriction to flow in the pipework.
no drop off over time indicates that pressure is constant, so unlikely there's serious fouling in the boiler heat exchanger.
if you turn the combi off, so running cold water straight through, what are the timed sets then? do both hot and cold sides again
..and don't worry about two decimal places...