How long will the socket opening in the soil for the5-Gallon Grounder last before the field needs to be tilled or sub-soiled?

There is no precise answer here as soils are extremely variable. However, if you suspect that the soil is becoming sufficiently compacted to restrict oxygen and inhibit root growth and drainage, do a perc test. Simply remove the container, fill the hole with water, wait about 30 minutes and fill the holes again. If the hole is still holding water after 24 hours, it flunked the perc test and actions should be taken at the earliest opportunity.