Every machine was different (I guess due to the other components in the 41 as well as mfg. variations) but as I recall, for my 41CX drift was about 1 minute in a month or so, but only as compared to other time sources which were not absolute either. In the military, I occasionally had access to 'official' clocks, but being official did not mean they were necessarily accurate.
Before PCs had access to time servers, NIS-managed cesium clocks, etc. all clocks varied, we just never knew. Or cared.
Leaving obsession and other personality quirks aside, I can't think of a reason the clock in a calculator would ever need to be more accurate than the levels being reported here. 6 minutes in a month does seem like it could be noticeable, but only if you compare it to some other time source you know is better, in which case you have access to a time source you know is better, and can adjust the DM42. So, no problem, right?