I have to admit that 3 hrs seems excessive, as always I have to say that I was not there and there could be a number of considerations missed.
If they lost the green fluid then it's likely that the yellow system was lost due to the PTU running and causing an overheat. Maybe during the takeoff inhibit phase.
They may have waited for this to cool to recover systems before making an approach.
I wouldn't like to land with accumulator only pressure, regardless of how long the runway is.