your description of reasoning , methodology, time allowed and credible considerations are all aiming at best practice and superb developments.
If you make the biochar you may like to quench and soak the char in the urine at the earliest (hot, warm, ultra-dry) stage. The follow the process as you outlined.
Have lots of productive fun and please take photos of the effects your Biochar process has on the production in the garden and on the land to share here with the network/ discussion group.
Best regards and thanks for sharing
The purpose of using urine-soaked biochar is to recycle nutrients and charge the dry, sterile biochar.
First, I mix in active compost with the sterile char so there are hungry microbes lurking when the urine is poured through the mix.
Second, the container is large and has small holes in the bottom allowing the excess liquid to slowly drip out the bottom. You will find contaminated water strained through charcoal comes out mostly pure as the nutrients are stripped from aqueous solution to reside within the biochar.
Third, this charged biochar is then mixed into the rough side of my compost pile which helps preserve the detritus from gassing off as it rots while also integrating with the other soil microbes.
Fourth, the working raw pile of compost is turned into a finished pile of compost to sit until cool.
By the time this material is applied to the garden soil, the microbiology has done its magic. No worries. Aerobic compost has a healthy smell with dominant non-pathogenic bacteria that have their way with the bad bacteria.
If plated and isolated very carefully, healthy soil probably contains something of everything in its makeup. Immerse into this biological cloud sans mask and gloves. Eat the occasional raw beet, carrot, or potato fresh from the garden with a patina of dirt. It's all good.
Just do it because it is the right thing to do.
Does biochar charged with urine need to be stored for a month before application?
The WHO recommends that urine to be applied as fertilizer on food crops that are processed should be stored for a month to kill pathogens. Urine should be stored for six months for crops that are eaten raw. Is there a similar storage requirement for biochar charged with urine (or manure)?