> 1a. A quick look at that last glacial maximum shows time frames on 10’s of thousands of years. So the ice would be accumulating for around ~10-15 thousand years then declining to where we see it today possibly.

A fair bit too quick for the ice accumulation phases. 10,000-15,000 years sounds more like the length of an interglacial, ie. what we’re in right now. It has always taken several times the length of an interglacial to transition to the next glacial maximum (though transitions back into interglacial are typically more abrupt). Maybe you are reading the graphs the wrong way around? 15,000 years is about the length of the phases in the last million years when going from glacial to interglacial.

Even before the Mid-Pleistocene Transition — before the glacial-interglacial cycle started turning from a 40,000 year cycle into the current 100,000 year cycle — it was taking at least 20,000 years to get from minimum to maximum ice volume.

For the last million years or so we are within the territory of the 100,000 year cycle, with much more drawn out changes (at least going from interglacials to glacials). For instance the previous interglacial ended about 115,000 years ago and the last glacial maximum began about 30,000 years ago.