Typically you spend a year doing each promotion, so it would cover 2 years to do those 2 levels. It's also normal for the County FA to require you to have done a decent quantity of matches in the preceding year - they will say 20, but won't hold you to that too strictly if you qualify part way through a season and only manage 15 or so.
Some CFA's will offer the option of a double-jump, doing both promotions in one season - literally requiring twice the number of matches, observations etc. But that's often a bit frowned on.