Impeller Change Interval

Shoehorned in.
Not enough space to slide the impeller out, the entire water pump has to be removed.
Wish it was not so..

Indeed, it

The set is not always a big problem since centrifugal force helps spread the blades a bit
looks like a spring start up rip, or a solid. That's why I asked if there are racors or a basket on the intakes

It sounds like you're talking about the Speedseal impeller cover. Their website says that they are having to close their business "due to continued illness."

Yes Dear.
I looked at accessibility before I purchased the tub, and it looked ok, but you won’t know until you actually do something, water pump, impeller, zincs, whatever.
The Albin 28TE comes in 2 versions, flush deck, or engine box: The most accessible is the engine box, my version.
Everything is doable, but not easy. Probably the same with every boat made by mankind....

What was easy to get to 20 years ago, ain't so now - my aching back. I thought nothing of being upside down back then with a plier and a screw driver. Today I need the correct tools, time , patience and a comfortable position. If it take me 3 hours to do what I did in a hour years ago, so what. Enjoy the voyage, I say.

Yes it helps reduce the work by 3 seconds. But that's the nature of our current lives?? I have about 10 nuts, but so what! My Westebeke genny has 4 screws and take about 5 minutes to open and look in and refasten. Right in the front and fully accessible.

Do impellers bought as spares have a shelf life by which you need to install or throw them out?

Yes, it depends on how they're stored. But lets say in a climate controlled area, probably 10 years......maybe less. They're rubber/nitrile etc. so eventually they will dry rot, get hard, etc.

Vacuum bagging helps.