Some of this is on my website, some in other writings, and some not yet clear. I know Alex doesn't like some of the uncertainties, but they're hard to remove overnight.

(Yes, I know I've had 4 years now, but Rome wasn't built in a day, especially given I have to take time out to earn money in my day job)

The piece I did for LPSC about Aromatum Chaos discusses timeframes. That particular chaos zone some 80 km long by 50 km wide by 6 km deep was probably excavated in a single collapse and flow episode lasting between 6 hours and a week. Probably a couple of days.

other channels access more than one chaos zone and may have had multiple such episodes over a period of up to a few million years, with big pauses in between.

Aromatum pdf

I believe that Mars was originally cold enough for thick dry ice permafrost even at the equator. As it warmed (the Sun is getting hotter, you know?), the CO2 melted, with a bit of help from volcanic heat. This part of the story needs a lot of work yet.

Liquid CO2 can sit in the subsurface for quite a time before it has to do anything, providing there is a layer of normal ice sealing it in.
Stuff on liquid CO2

There probably is a slow cycle of melting of dry ice at the base or edges of the polecap, which weakly resupplies the subsurface.