Since there is still ammonia in your aquarium, I would not bother fertilizing nitrogen until the ammonia is gone (plants preferentially uptake ammonia to nitrates for a nitrogen source).
Phosphates, trace mix and other nutrients (potassium if you are dosing it) can be dosed immediately.
Yeah you're right. Nitrates are 20ppm which are like okay for N.
A tank consists of a series of cycles, ammonia, nitrates, nitrides themselves must cycle in addition to all the bacterial, enzymes etc which must be given time to develop. Water changes are used to keep levels from spiking to prevent harm to fish and other livestock. if this is a plant only tank, there should be no reason why dosing could not start today for the plant development and intake of NPK should run independantly. If you are cycling with Ammonia however, the risk of getting plants burned is a there as it is strong so be mindful of dosages over the days/weeks until the ammonia levels gradually diminish.
Nitrogen cycle I know about and so adding Seachem stability too. But what i dont know is about enzymes cycles. So shouldnt I change the water evryday ? I mean I was changing water just to keep the ammonia level under control. I will change 50% water every 2 or 3 days now. And I have started dosing micro, P and K now. Nitrates are enough to keep the plants go.