S23 Astro Mode exposure time

[MitchG]

Can anyone explain a bit of detail on the S23 Ultra Expert Raw Astro mode (multi-image stacking and adjustment for star trailing)? I understand the concept but would like to understand a bit more detail. For example the image below of the Big Dipper (upside down at left) pointing to Polaris (North Star at lower right) shows in the info field a time of 4" 1/2 sec 

(it was a 4 min exposure setting). This was for the X1 Camera with a Freewell X1.7 telephoto in front. (I'm sure that in the past, using the x1 S23 camera had an exposure time of ~ 20 sec so surprised to see it at 4" now with the 1.7 lens added in front). That time of exposure I presume is the individual shot exposure.