For reference, here's what I've got:

-2.5' kishu mandarin
-2.5' ficus lyrata (2-stemmed)
-jasminium sambac
-2 croton plants (Codiaeum)
-small heather plant

The problems and likely culprits:
-fungus gnats infesting each plant (despite my very conservative watering)
-leaf drop on the kishu (prob. low-light related)
-soil compaction/exposed roots on jasmine

All plants but the fig are planted in 5-1-1 mix which I must have seriously screwed up given the gnat issue and the PWT. I think the bark pieces I used were too large for the rest of the mix. This might also explain the exposed roots on the jasmine.

The fig is just in standard houseplant (water-retaining) mix because I purchased it a few weeks ago and wasn't sure whether to repot or wait.

Thankfully none of the plants appear to be diseased or nutrient-deficient but the gnat infestation and not-quite-right soil seem to be causing stress.

So - I've assembled 2/3 of the ingredients I need for gritty mix (Turface and granite, still looking for bark fines) and am very eager to repot each plant in it so as to maximize their potential and remove/reduce the gnat problem. But this generally isn't the best time of year to repot.
Which is worse? Disturbing the plants by repotting now?
Or letting them languish in substandard conditions until spring?

If it makes any difference: currently the plants receive bright, indirect like all day from large North and East facing bay windows.
I was considering moving some of the more sun-craving ones to my office next month where they can benefit from southern exposure and slightly warmer temps.

So should I act now?
Or do I need to sit on my hands and remember the difference between "plant time" and human time?

Any help would be appreciated!
Let me know if any more info would be helpful.

As example, I was recently forced to re-pot an orchid that was drowning in decomposing medium that stayed too wet. The roots were literally rotting. I had no choice but to un-pot, trim the roots, use an anti-fungal, and re-pot using fresh medium. I couldn't wait for spring, or I'd risk losing the entire plant.

I have other plants that I know need re-potting for one reason or another, but none of them are in desperate need. I'll wait until spring for every other plant.

And yes, there are a few things required when moving plants from regular potting soil to a more sharp draining, gritty medium. It's wise to study the concept well, and understand what is required before proceeding. Bare-rooting is required, and it's best not to take any shortcuts when preparing the medium. Before I began, I read over the material several times, and I did some forum reading to ensure I understood the concept behind the mix and everything that I might need to adjust for.

Josh

On the gnat front, I've ordered BTi, sprinkled some Diatomaceous earth on the soil, and have some perlite in reserve to throw on top as a barrier layer if all else fails.

The kishu might continue to lose leaves (due primarily to temp/low light, I think, since remaining leaves and branches look green and healthy), but it sounds like I should just suck it up and wait until spring unless it deteriorates significantly further.

For the jasmine, I'll add some more growing media to the pot to cover the exposed roots and do a repot in spring.

The outstanding question is the fig. Health-wise I think it'll be fine to wait and repot in a few months. But right now there are 2 stems growing in the small pot. Ultimately I'd like to separate these two and plant them in 2 pots, but I know that'd be a difficult task if their roots are fused/tightly bound together. Will the 3 or 4 months that pass before repotting make this task significantly harder?

Or is root growth so slow (esp in winter, indoors) that there'd be little difference between now and then?

Thanks for all your help and support.

-Michael

When I re-pot my fig, I do some heavy root-pruning; and so I think you needn't worry about
carefully separating the roots of the figs - just blast away the old mix, and then cut the roots
apart if they don't untangle willingly.

In my particular area, figs don't leaf out until late March or early April. Looking over pictures
I've taken of the process, I see that I've re-potted my fig during the last week of February
for the past two years.

Josh

Of course, one could always go to a reliable insecticide or use those dunks for pond mosquitoes, etc...

Despite having a fast-draining soil and watering infrequently, the fungus gnats weren't going away. I finally spread some diatomaceous earth on the soil surface which seemed to keep the population in check for about two weeks; when I started seeing the gnats again I took the additional step of adding a thick layer of coarse perlite on the surface which seems to be working for now.
I bought some mosquito dunks/BTi and will use them as a final measure.
(I'll be glad when the war is over!)

When it is eventually time to repot I'll use gritty mix for most of the plants and hope that solves the gnat problem for good.
For now, the plants seem to have stabilized.