How long before your cartridge warms up?

There is no rule, even not for room temperature. You will find cartridges which need a "warm up"the way you describe, a definite room temperature, some are very sensitive to VTF, some need 5h to "break in", some 50h and so on and on...and there are others which do not need that.
Mine for example are ready to go for 100% from scratch. Except the Lyra Titan i / Olympos, those demand a nice room temperature :-)

Two LP sides (40+ minutes) sounds like a long time to me. Are you sure this is all due to the cartridge? Was the rest of your system already warmed up?

In my case, using a Benz LP, the cartridge seems to be fully "warmed up" in something like 5 minutes. Initially it sounds a tad bright but it settles down during the first few minutes and I really don't notice any more changes after that.

My electronics are a different story. My tube power amps sound a lot better after about 30 minutes, and I suspect that one of them sounds even better after a couple hours, but it is hard to judge that kind of change over a long period like that.

I agree with all that is being said here except that I don't think 40 minutes is excessive. I did note Mike Fremer at the latest Axpona stating that he finds his cartridge needs about 4 sides before it is at full stride.

I think what I experienced was an abnormal difference in the recording quality of a track on an album which was new to me; my subsequent testing today would indicate that my Anna does not need a wam-up period.

My Graaf amps are another story, the GM200 need about 30 to 45 minutes, the Modena (signature version of the original Graaf GM20) can take up to 2.5 hours to be at its complete best.

I did adjust the VTF already as the warming weather audibly necessitated that change. I believe, that was done about 4 weeks ago.

I give my amp and phono stage at least 15 to 20 minutes before I play my system. I have a zyx diamond gold and it sounds the same from first touch to the end of session. I recently replaced my benz micro lps which needed at least a side or two to sound its best. Best of Luck

Most of the edge on my OC-9/II is gone after about half a side. It mellows for a little while after that.