If you can attack with enough force to kill all the occupation fleet your base can be freed of the occupation. When the enemy fleet is destroyed a final attack will cause a Revolt, and free the base. If you do not make that final attack the revolt will happen eventually anyway.
However, there are lasting effects from the occupation situation.
Defense Regeneration[]
Following a successful revolt your Defenses will begin regeneration. They repair themselves 1% automatically every hour until unrest decreases from 50% to 40%, when the base gets all the defenses restored. (It can now be occupied again and use the JG again).
It does not matter how much, or how little, defense you had, 4 Planetary Rings will return just as fast as 1 Barracks. Newly constructed defense comes in at the reduced rate too, so if you finally complete that PRing right after the base is freed it will come online at 1% and grow.
Economic Regeneration[]
Your economy will slowly return to its full level too. It regenerates by 2 credits per day automatically until it reaches the normal economy.
The base screen lists this as - Economy (the full amount) and Owner Income (reduced amount)
As the Help Screen states: "An occupied base has 30% less construction capacity, 50% less production capacity, and 30% less research capacity, in addition to the 30% reduction in the base's economy."
While production, construction and research return to 100% when the base is freed, the economy creeps back at 2 credits per day. Because the amount lost is 30% of the total, the recovery is longer for higher level bases.
For example:
A level 50 economy is reduced by 15 by an occupation, It will take 8 days to return to level 50.
A level 100 economy is reduced by 30, and will take 15 days to reach 100 again.
If you add an economy structure it will increase the owner income, or current reduced economy, as well as your total Economy level. Thus it does not reduce recovery time, but it does give more credits per hour from then on.
It is unclear when a "day" begins, it may be at 00:00 server. If so, freeing your base at 23:59 server time is better than waiting to 00:01.
If the base was a Capital freeing it removes the 15% penalty from your Empire Income. The base income/economy will recover at the standard 2 credits/day rate.