The Tropical Fruit Forum

In my experience, I budded a seedling scion wood to 5 year old Flying Dragon. These FD stocks had nearly all flowered fruited at this age.
The FD trees budded with the seedling grew well and promptly flowered and fruited.
The original seedling has not yet flowered.
The FD trees were in 5 litre pots, so bigger than the usual FD seedlings, but not overly large trees,
i.e. it was not like top working a big rootstock.
Mostly Citrus are grafted to young immature stocks, so this wouldn't show up.

I think it is worth investigating grafting onto early flowering rootstocks.
Since the fast flowering trifoliata is a small plant, you may lose some vigour ??
There may be a chemical/hormone flowering factor transmitted to the scion from the flowering aged stock.
Most Citrus are complex hybrids of several "species", there may be competing genes for flowering time.
This may be why there is no clear answer to advancing flowering time, but many anecdotes.
Also it may not work equally for all Citrus types, depending on the ancestry.

"Looks like a large kaffir lime."

Looks like Citrus macrophylla,
and since it's related to KL I can see why you said that.
It is a rootstock variety in USA, so could pop up from suckers or failed grafts.
The foliage doesn't have the double leaf / enlarged petiole of KL or other Papedas.

Here is some Low Biuret Urea application info from an Australian company
https://www.incitecpivotfertilisers.com.au/~/media/Files/IPF/Documents/Use%20Directions/Use%20Directions%2002%20Liquifert%20Lo-Bi.pdf
This product would have to be sourced from a farm supply shop.

Fingerlimes have a tendency to produce numerous male flowers and drop fruitlets. It's probably more certain to pollinate into a good fruit setter like Rangpur, Calamondin etc to recover hybrid seed. If you are not particularly keen on producing a "Lime", a mandarin or Blood orange might also be a good seed parent.

Here is the info from the PVR patent application

Origin and Breeding Open pollination: ‘Australian Blood’ lime was identified from progeny of open-pollinated seedlings grown from seeds of a zygotic seedling of Rangpur lime grown adjacent to a row of Citrus australasica var. sanguinea seedlings (red-flesh finger limes). Rangpur lime is a citrus rootstock cultivar that yields acid mandarin-like fruits. It has the botanical name of Citrus x limonia (Watson et al, 1984). The seedlings from which the ‘Australian Blood’ lime was identified were culled from other seedlings of the zygotic Rangpur lime seedling based on the obvious Citrus australasica habit and characteristics that they displayed. As a consequence of these characteristics, it is assumed that the pollen parent of the Australian Blood lime was a seedling of C. australasica var. sanguinea. The seedlings with C. australasica habit and characteristics were rowed out for field evaluation and monitoring for growth habit, fruit yield and characteristics. The Australian Blood lime was selected in 1990 when 12 trees were propagated as rooted cuttings for further evaluation. Selection criteria: it was selected for the culinary qualities of its striking red, highly aromatic acid fruits. ‘Australian Blood’ lime will be propagated vegetatively by grafting or budding to standard citrus rootstocks.
Breeder: Dr. S.R. Sykes, CSIRO Plant Industry (Horticulture Unit), Merbein, VIC.

This info from here, http://www.gondwananativelimes.com.au/australian_native_red_lime.html

Some other articles say that Ellendale Mandarin is the other parent. Not sure why this is reported.

There are a couple of assumptions in the above, i.e. that a red Finger lime was the parent, assumed because the Blood Lime has red pigmented fruit.
This may not be 100% correct, as another non red/red Finger lime could possibly contribute red genes to an orange fruited Rangpur.

As far as I know some of the Finger Lime parents used by CSIRO came from from the USA collections, possibly seed introductions.
I did grow one of these Finger Limes some years ago, from CSIRO budwood. It was a cherry red small fruit, with cherry flavour.
Not sure if that was the assumed parent.

ps The CSIRO Merbein is now closed. Not sure if the PVR patent has expired yet ??
I once saw some F2 selections from Blood Lime at a Farm Field Day, looked like bigger bumpy finger limes.

As I can get plenty of the classic Citrus around here from farms, (Oranges and Mandarins), the Sanbokan is a standout for me. I really enjoy the sweet lemon flavour.
It also has a fragrant element that you can't get from just adding sugar to Lemon Juice.

I think it was discussed on the forum here ?
https://tropicalfruitforum.com/index.php?topic=45565.0

For severely neglected trees, nearly any fertiliser should get a response.
I would probably first go for a low to medium N, organic based, to give some soil microbe stimulation. Or at least include some soil stimulation.
As for pruning, you may as well remove any damaged growth etc, rather than resurrect the tree with it still there.
For plants with previous heavy leaf loss, maybe prune back the top third, especially naked twigs, rather than trying to get every bud to flush.
Sometimes heavy flushing on tired plants leads to growth stagnation.

Personally, I don't think there are health concerns using urine for plants. It is essentially sterile.
It has emergency medical uses, with mid stream urine, i.e. suburn, as urea itself is skin moisturising.
As Galatians said, the N Urea content of Urine is far lower than Fertiliser urea, so it can't be used to make the equivalent concentration sprays.
That said, fertiliser Urea has a lot of problems with loss of N to the atmosphere, so often the effective ammount the plants can get is lower than that applied.
Not sure if more frequent low % urine sprays will give the boost of the the N fertiliser Urea spray.
Biuret is produced by heating Urea in the manufacturing process, so shouldn't be a problem in Urine.
I have used diluted urine to feed weak plants or very small seedlings that I didn't want to risk with stronger fertilisers.
Also had some Citron seedlings with what looked like Biuret problems from fertiliser in old potting mix.
It seemed to correct them, possibly by gently lowering the Biuret %  in the mix ??

According to UCR,
"Yuma ponderosa and Cuban Shaddock, are identical. However, the isozyme patterns differ."
So Its not A " Ponderosa" lemon.
Still Ponderosa is probably your best bet.
Can't see why Trifoliata wouldn't work either.
You are trying to save it, you can always graft onto something better down the track.
https://citrusvariety.ucr.edu/citrus/yuma_ponderosa.html

I grabbed a leaf off my Oroblanco, and it looks very similar to your plant, can't see any major differences.

The nice red color is inherited from Flying Dragon, normal Trifoliate and its hybrids have only yellow-orange autumn color.

Rootstock seedlings of the same strain of normal trifoliata are fairly variable as to autumn colour, and to some level when they change colour and how long they hold autumn colour. Weak seedlings, off types and runts can be clearly different in their colour and timing of change.
There are some oranges and reds possible, even verging on maroon.
Stressed or neglected trees, underfertilized etc can also turn colour earlier.

Looks like an interesting project overall, Citrus and vegetables.