Hi Bonzi
I know absolutely nothing about Serissa. But there is a joke among the international bonsai people of a common post that states. Help bought a Serissa bonsai from the markets and it is dying. Apparently this happens after the tree is already dead. Luckily you have come here before that and your tree still looks quite healthy
Most trees/bonsai do not do well inside but like I said I have no idea with Serissa and Shibui is very learned in many species so I will also wait and see what the advice is.
Some people suggest that dunking a pot in water like you suggest is not the best way as it will not wash the salts out or in other words freshen the soil by flushing water though the pot.
I have never agreed with that as long as you are dunking it in water that goes over the top of the pot then I can see no reason why this would not also flush the soil fresh. It is a good idea to maybe dunk the tree a couple of times. Let it soak for a while if you wish but when you take it out lift it up, let it drain and then dunk it again, drain. It is hard to give a schedule for watering as there are many variables. The best basic advice we can give is saturate the soil when watering but then do not water again until almost dry.
I keep several trees inside over Winter and I find dunking in the kitchen sink a practical way to water. You can let the tree drain on the sink top for say 10 minutes and then place on any furniture without a drip tray as no more water will drain from the pot after this.
Believe it or not
Good luck

It's too bad your in such a hurry cause the stories I could tell you, Bushels and baskets of stories, hole crates full of stories. But if you can spare a moment I will tell you one story.