Do I have to wait more than one year before turning that plot into clover again?
I didn't notice exactly when you planted this plot?
Maximum nitrogen fixation/production is achieved after approx. 6 months if clover is kept clipped when it flowers but that doesn't mean there aren't positive N gains in 3 months for instance.
I'm not sure of all of the reasons why clovers don't last longer, they can be maintained longer with herbicides but eventually they tend to die out with white clovers lasting longer then red clovers.
I like to divide any given plot (regardless if it is the size of a garden or 20 acres) into 1/3rds and keep a constant rotation of 1/3 clover, 1/3 brassicas and 1/3 fall cereal grains. When the clover plot is wearing out, I follow it with brassicas and reseed the clover in the cereal grains.
In this manner you ALWAYS have clover, always have a winter attractant via the winter rye and always have brassicas that can produce maximum forage production.
Doing this means you don't have all your eggs in one basket and you provide deer and wildlife with a year around food supply and keep your soils healthy.
On larger plots corn could be used rather then brassicas.
There really is no reason not to have everything all the time versus..."all or nothing" (gee...if I plow down my clover I won't have any for a year"
No one crop provides year around feed at least in the midwest and northern areas and soils become diseased when one crop is planted repeatedly for years.
You might explore the option that crop rotation can give you to better achieve your goals more effectively by reading my threads that will also help you understand when to till under clover and why.
Cereal Grains and Cover Crops