that is an interesting question as the nutrient levels will decrease over time. However the humus content stays high for longer, so old compost will still be an excellent soil improver. [in other words I don't know haha!]

Home made, or from the garden center, Merlinbabydog?

I meant home-made Tug. I've used it recently but wasn't sure whether the microbes will still be active.
A soil improver will do for my purposes. so thanks SBG.

Depending on temperature and humidity, the more sensitive organisms will die within a week of being removed from the compost bin. Most of the others will survive as long as the compost feels damp, up to a month or two. A small fraction will form spores or lay eggs, and survive that way as long as the compost isn't exposed to killing heat--about 72º C.
Once dried, the compost keeps it's nutrient content permanently. If kept moist, the nitrogen content will gradually go down, as denitrifying bacteria turn the nitrogen carrying compounds, which plants can use, into nitrogen gas, which most can't.
Through it all, most of the greater bulk of the compost, cellulose and it's breakdown products, remains available to improve soil structure, and feed soil organisms. Small amounts are lost through decay, finally, into carbon dioxide and water.