Hi James
It depends which bit of the process as to how quick.
When I was exploring the many variations on slope and crossover point I used my DSP. I could just drag the crossover point or type in a new value from my laptop at my listening position. When I upload the new values to the DSP unit (while music is playing) there is a short break of 1 maybe 2 seconds while it takes effect, so it is fairly instant.

When comparing bass drivers I have both types set up with the same type of cable running to the back of the power amp, which is out into the room, so as long as it takes to unplug one set of banana plugs and insert the next. I do this while music is playing, not the best thing to do, but it makes it quick.

When comparing the all passive to the partly active/passive I had two set ups inside the Yamaha cabinet, the original passive crossover and a lash up similar to my proposed layout, using cheap caps and some old coils I wound down to the needed values and stuck them with hot melt to some 6mm MDF. I used my 3-way backplate with 3 sets of terminals (from my fully active experiments) and had the two options available by swapping banana plugs at the back of the speaker. This took a little longer, but again I did it hot, so not too long. The results were so obviously in favor of the semi-active I modified the original x-over strait away, so I could take advantage of the better parts used. Nothing that can't be easily reversed, just unsoldered one leg.

All parts were well run in before comparison.

I got the Celestion 66 as good as I could, but still wasn't happy.

I can spot what I'm looking for pretty instantly, I've been trying to resolve this and find a set of speakers I feel comfortable with, for many years. I hear new gear at shows, that sounds terrible, its ok with instrumentals, which is what they tend to demo, but stick some well recorded vocals on and they are anything but natural or realistic with a horrible edge to the end of words, not sibilance, I can't stand that either, it's I suppose, the equivalent at the other end of the scale. I've heard very few multi way speakers that I could say were good enough and even fewer I could afford. I've heard quite a few two ways that bettered most of them and for a lot less money, the trade off being a lack of deep bass. Some speakers that don't exhibit these faults are just to soft and rounded off for my taste, many of the JBL models fall into this category, but many are happy with that sound.
Maybe I'm just being over fussy.
The distortion just gets in the way of my enjoyment, I know that someone sat in front of me wouldn't sound like that and I know there are speakers out there that can achieve it. So my quest continues.