Since Fall is impending but I still have roughly three million man-hours of tuck pointing before me, I Googled "mortar temperature range" and found a page on cold weather masonry. The upshot: 40 degrees (F) and up, I'm fine. Below that, things get tricky, so I'm just not going to mess with it; it's not like there aren't plenty of things to do on the inside of the buildings.
But it occurs to me that the utter need for tuck pointing in the big house is another serious flaw in its heatability quotient. Cracks in the outer wall equate to drafts on the inside of the house. So ultimately, tuck pointing is going to be absolutely necessary over the coming year.
The other topic in the world of brick that has occupied me of late is how to seal the bricks before the weather. Most of my bricks are still in incredibly good shape for baked clay that's been out in the weather for 120 years, but some are not. Turns out people use a sealer on bricks nowadays, and I think it makes sense.
Opinions differ, but the key is that a sealer for masonry has to soak into the brick and chemically bond with it, while not sealing off all the pores (water vapor inside the house has to be able to escape, or it can freeze within the brick, leading to spalling). There are two camps: the silane/siloxane camp and the silicone camp. Silicone tends not to penetrate the brick as well, but there are some silicone masonry sealers that do, and if they do, their lifetime tends to be far better than the organic silanes and siloxanes. Better enough, actually, that they don't have good data yet, because their test masonry hasn't degraded enough yet. That sounds about right to me.
There's a decent link here (Masonry Magazine). A silane/siloxane link is here - silicone-based sealers operating with stearate would be an example of something Not Good. (I'm guessing Thomson's Water Seal is one of these.) It's OK for wood, but not masonry.