Is it too late to give them some nitrogen?

You could feed them for a week and go for another 3 weeks with fresh water or feed them fresh water for the next 2 weeks.

Ideally, you should maintain the same NPK ratio throughout the crop (until the final flush). Whether it's growth or flowering, I use my tri-part in the same way, with only the additives fluctuating according to the phase. Nitrogen is not to forget, because even if it's less important, it plays a part in the life of the plant and helps the buds to grow (Overdrive from ADN even adds a little Nitrogen to the mix to make the flowers huge).

At this stage of the growth adding Nitrogen will be useless because the roots won’t process it. Your plants are actually in bloom, the roots are processing Phosphorus and Potassium.

I have a strawberry banana fading sooner than I would of liked so I added some grow nutes to the feed last time I watered which was 2 day ago and I have 20 days left. My feed strength is 1030ppm and an ec of 1.9-2

Wouldn’t add any nutrients. The buds will get what they need from the leaves at this point which is the change in color.

If they are alive, they will use nitrogen as needed... so, sure... give them some N It is an absolute myth that you need to drastically drop N concentration in flower. Only in cases involving slow-release nutes or non-plant available N that requires microbes to get it plant-ready - this context has some lag between when you stop giving N and when it stops entering the plant in a useable form and you wouldn't notice any drop off in N entering the plant even if you cease providing it for a bit, but eventualyl it will definitely need it in near-vegetative phase proportions. N is used in the nucleotides that make up dna. it is in all sorts of other bits of anatomy the plant needs to reproduce in order to continue cellular growth. It is essential. Several studies show that mariuna plants use a good amount of N in flower phase despite the dropoff of stem elongation and new leaf growth. It is absurd to continue to deny evidence based findings in lieu of anecdotal knowledge created by people with major gaps in relevant knowledge base that were never tested or verified. never bothered to use existing knowledge to help form such conclusions... just had some esoteric result in their basement or garage and repeated it frequently and loudly that others followed the herd, lol.

If the buds are done growing I would not give it anything at this point. The plant will consume all the leaves before it goes for colas. If they are then a light nitrogen heavy potassium feed. Looks like you got about a week left. I personally woukd not worry about it.