A day or less

Few days or weeks.

Months or years

Not complicated: Simple

Not too complicated.

Might be complicated.

Probably easy

Not too difficult.

Might be difficult.

May not need a plan.

A plan might be needed.

Most likely a plan will be needed.

Might have an age requirement.

Might require going to a special school, possibly for a long time.

Might require some sort of college degree.

Might require getting some sort of license.